Bug 414965

> Error loading plugin "kcm_desktoptheme" "The shared library was not found." 
That means there's a problem with your installation. Please report this to the Solus folks.

I have to reopen this, I checked it with the devs from Solus and we checked it as well with kde neon unstable Edition (fully updated) and it throws the same error as well.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: KDE neon unstable Edition 
(available in About System)
KDE Plasma Version: 5.17.80
KDE Frameworks Version: 5.66
Qt Version: 5.13.2

Strace from KDE neon

stat("./kcm_cursortheme", 0x7ffeae4a6af0) = -1 ENOENT (No such file or directory)
stat("./kcm_cursortheme.so", 0x7ffeae4a6af0) = -1 ENOENT (No such file or directory)
stat("./libkcm_cursortheme", 0x7ffeae4a6af0) = -1 ENOENT (No such file or directory)
stat("./libkcm_cursortheme.so", 0x7ffeae4a6af0) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu/qt5/plugins/kcm_cursortheme", 0x7ffeae4a6af0) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu/qt5/plugins/kcm_cursortheme.so", 0x7ffeae4a6af0) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu/qt5/plugins/libkcm_cursortheme", 0x7ffeae4a6af0) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu/qt5/plugins/libkcm_cursortheme.so", 0x7ffeae4a6af0) = -1 ENOENT (No such file or directory)
stat("/usr/bin/kcm_cursortheme", 0x7ffeae4a6af0) = -1 ENOENT (No such file or directory)
stat("/usr/bin/kcm_cursortheme.so", 0x7ffeae4a6af0) = -1 ENOENT (No such file or directory)
stat("/usr/bin/libkcm_cursortheme", 0x7ffeae4a6af0) = -1 ENOENT (No such file or directory)
stat("/usr/bin/libkcm_cursortheme.so", 0x7ffeae4a6af0) = -1 ENOENT (No such file or directory)
write(2, "org.kde.kcoreaddons: Error loadi"..., 243org.kde.kcoreaddons: Error loading plugin "kcm_cursortheme" "The shared library was not found."
Plugin search paths are ("/usr/lib/x86_64-linux-gnu/qt5/plugins", "/usr/bin")
The environment variable QT_PLUGIN_PATH might be not correctly set
) = 243
stat("./kcms/kcm_cursortheme", 0x7ffeae4a6b60) = -1 ENOENT (No such file or directory)
stat("./kcms/kcm_cursortheme.so", 0x7ffeae4a6b60) = -1 ENOENT (No such file or directory)
stat("./kcms/libkcm_cursortheme", 0x7ffeae4a6b60) = -1 ENOENT (No such file or directory)
stat("./kcms/libkcm_cursortheme.so", 0x7ffeae4a6b60) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu/qt5/plugins/kcms/kcm_cursortheme", 0x7ffeae4a6b60) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu/qt5/plugins/kcms/kcm_cursortheme.so", {st_mode=S_IFREG|0644, st_size=251320, ...}) = 0
openat(AT_FDCWD, "/usr/lib/x86_64-linux-gnu/qt5/plugins/kcms/kcm_cursortheme.so", O_RDONLY|O_CLOEXEC) = 17
fstat(17, {st_mode=S_IFREG|0644, st_size=251320, ...}) = 0
fstat(17, {st_mode=S_IFREG|0644, st_size=251320, ...}) = 0
mmap(NULL, 251320, PROT_READ, MAP_SHARED, 17, 0) = 0x7f4a88049000
close(17)                               = 0
munmap(0x7f4a88049000, 251320)          = 0
stat("/usr/lib/x86_64-linux-gnu/qt5/plugins/kcms/kcm_cursortheme.so", {st_mode=S_IFREG|0644, st_size=251320, ...}) = 0
lstat("/usr", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/usr/lib", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/usr/lib/x86_64-linux-gnu", {st_mode=S_IFDIR|0755, st_size=118784, ...}) = 0
lstat("/usr/lib/x86_64-linux-gnu/qt5", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/usr/lib/x86_64-linux-gnu/qt5/plugins", {st_mode=S_IFDIR|0755, st_size=20480, ...}) = 0
lstat("/usr/lib/x86_64-linux-gnu/qt5/plugins/kcms", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/usr/lib/x86_64-linux-gnu/qt5/plugins/kcms/kcm_cursortheme.so", {st_mode=S_IFREG|0644, st_size=251320, ...}) = 0
openat(AT_FDCWD, "/usr/lib/x86_64-linux-gnu/qt5/plugins/kcms/kcm_cursortheme.so", O_RDONLY|O_CLOEXEC) = 17
fstat(17, {st_mode=S_IFREG|0644, st_size=251320, ...}) = 0
fstat(17, {st_mode=S_IFREG|0644, st_size=251320, ...}) = 0
mmap(NULL, 251320, PROT_READ, MAP_SHARED, 17, 0) = 0x7f4a88049000
close(17)                               = 0
munmap(0x7f4a88049000, 251320)          = 0
openat(AT_FDCWD, "/usr/lib/x86_64-linux-gnu/qt5/plugins/kcms/kcm_cursortheme.so",


Strace output from my Solus system

Strace:
## Search for KCM
statx(AT_FDCWD, "./kcm_cursortheme", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "./kcm_cursortheme.so", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "./libkcm_cursortheme", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "./libkcm_cursortheme.so", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "/usr/lib64/qt5/plugins/kcm_cursortheme", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "/usr/lib64/qt5/plugins/kcm_cursortheme.so", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "/usr/lib64/qt5/plugins/libkcm_cursortheme", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "/usr/lib64/qt5/plugins/libkcm_cursortheme.so", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "/usr/bin/kcm_cursortheme", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "/usr/bin/kcm_cursortheme.so", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "/usr/bin/libkcm_cursortheme", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "/usr/bin/libkcm_cursortheme.so", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
org.kde.kcoreaddons: Error loading plugin "kcm_cursortheme" "The shared library was not found." 
Plugin search paths are ("/usr/lib64/qt5/plugins", "/usr/bin") 
The environment variable QT_PLUGIN_PATH might be not correctly set

## Now it's 'not found' search for KCM adding kcms/ to path and work as expected
statx(AT_FDCWD, "./kcms/kcm_cursortheme", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "./kcms/kcm_cursortheme.so", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "./kcms/libkcm_cursortheme", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "./kcms/libkcm_cursortheme.so", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "/usr/lib64/qt5/plugins/kcms/kcm_cursortheme", AT_STATX_SYNC_AS_STAT, STATX_ALL, 0x7ffc92db4f20) = -1 ENOENT (No such file or directory)
statx(AT_FDCWD, "/usr/lib64/qt5/plugins/kcms/kcm_cursortheme.so", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_ALL, stx_attributes=0, stx_mode=S_IFREG|0755, stx_size=215168, ...}) = 0
openat(AT_FDCWD, "/usr/lib64/qt5/plugins/kcms/kcm_cursortheme.so", O_RDONLY|O_CLOEXEC) = 17</usr/lib64/qt5/plugins/kcms/kcm_cursortheme.so>
statx(17</usr/lib64/qt5/plugins/kcms/kcm_cursortheme.so>, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL, {stx_mask=STATX_ALL, stx_attributes=0, stx_mode=S_IFREG|0755, stx_size=215168, ...}) = 0
statx(17</usr/lib64/qt5/plugins/kcms/kcm_cursortheme.so>, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL, {stx_mask=STATX_ALL, stx_attributes=0, stx_mode=S_IFREG|0755, stx_size=215168, ...}) = 0
statx(AT_FDCWD, "/usr/lib64/qt5/plugins/kcms/kcm_cursortheme.so", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_ALL, stx_attributes=0, stx_mode=S_IFREG|0755, stx_size=215168, ...}) = 0
lstat("/usr", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/usr/lib64", {st_mode=S_IFDIR|0755, st_size=172032, ...}) = 0
lstat("/usr/lib64/qt5", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/usr/lib64/qt5/plugins", {st_mode=S_IFDIR|0755, st_size=20480, ...}) = 0
lstat("/usr/lib64/qt5/plugins/kcms", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/usr/lib64/qt5/plugins/kcms/kcm_cursortheme.so", {st_mode=S_IFREG|0755, st_size=215168, ...}) = 0
openat(AT_FDCWD, "/usr/lib64/qt5/plugins/kcms/kcm_cursortheme.so", O_RDONLY|O_CLOEXEC) = 17</usr/lib64/qt5/plugins/kcms/kcm_cursortheme.so>
statx(17</usr/lib64/qt5/plugins/kcms/kcm_cursortheme.so>, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL, {stx_mask=STATX_ALL, stx_attributes=0, stx_mode=S_IFREG|0755, stx_size=215168, ...}) = 0
statx(17</usr/lib64/qt5/plugins/kcms/kcm_cursortheme.so>, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL, {stx_mask=STATX_ALL, stx_attributes=0, stx_mode=S_IFREG|0755, stx_size=215168, ...}) = 0
openat(AT_FDCWD, "/usr/lib64/qt5/plugins/kcms/kcm_cursortheme.so.avx2", O_RDONLY|O_CLOEXEC) = 17</usr/lib64/qt5/plugins/kcms/kcm_cursortheme.so.avx2>

To be clear, you're saying it has a warning line but everything works correctly?

(In reply to David Edmundson from comment #3)
> To be clear, you're saying it has a warning line but everything works
> correctly?

yes, it checks for the plugin inside the /usr/lib/qt/plugins path, triggers the warning but checks right after the warning inside the /usr/lib/qt/plugins/kcms path finds it and continues it. 

one of the annoying part is, it fills as well as my journalctl log with errors

This search paths issue was fixed a release or two ago.