SUMMARY
Impossible to make changes to build configuration. Changes made do not get written co CMakeCache.txt and ignored in builds. Reading CMakeCache.txt by KDevelop works fine. Changing it by hand wit text editor outside KDevelop allows to make necessary changes to build configuration. KDevelop will read changed file fine. Simply will not save changes to it. No error is reported. 

STEPS TO REPRODUCE
1. Open any project. Open configuration.
2. In Configure CMake Settings, Select Show Advanced. Show advanced values
3. Make any changes to any options - compilers, flags, etc.
4. Select Apply then OK, or simply OK.


OBSERVED RESULT
Changes are not saved. No error is reported. CMakeCache.txt is not changed. 

EXPECTED RESULT
CMakeCache.txt should be changed and build configuration updated. 

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: openSUSE Leap 15.3
(available in About System)
KDE Plasma Version: 5.18.6
KDE Frameworks Version: 5.76.0
Qt Version: 5.12.7

ADDITIONAL INFORMATION
OpenSuse installer did not originally include the indent package and KDevelop messages indicated that it was missing when configuration changes were attempted. I have installed the indent package. The messages disappeared but the problem with not saved configurations remained.

KDevelop logs following messages when started from console. None of them during changes of build configuration:

Connecting to deprecated signal QDBusConnectionInterface::serviceOwnerChanged(QString,QString,QString)
kdevplatform.shell: Can't load plugin "kdevghprovider" some of its required dependencies could not be fulfilled: "org.kdevelop.IBasicVersionControl@kdevgit"
kf.kio.core: We got some errors while running testparm "Weak crypto is allowed"
qrc:/qml/Develop.qml:139:21: QML Heading: Binding loop detected for property "font.pointSize"
qrc:/qml/area_code.qml:87:9: QML Heading: Binding loop detected for property "font.pointSize"
qrc:/qml/area_code.qml:63:9: QML Heading: Binding loop detected for property "font.pointSize"
kdevelop.plugins.welcomepage: "Last fetch of news feed was on Mon Jun 7 07:44:11 2021 GMT+0200"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevastyle" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevcustomscript" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevcustomscript" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevcustomscript" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevcustomscript" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevcustomscript" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevcustomscript" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevcustomscript" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevcustomscript" supports unknown mimetype entry "text/x-objchdr"
kdevplatform.shell: formatter plugin "kdevcustomscript" supports unknown mimetype entry "text/x-objc++src"
kdevplatform.shell: formatter plugin "kdevcustomscript" supports unknown mimetype entry "text/x-objchdr"