I can confirm this. It works fine on my desktop which still has Frameworks 6.0.0 but is broken on my laptop after upgrading to 6.1.0.

Confirmed, luks mounting is broken, meaning I can no longer access any of my backups, - or backup:
 
KDE Plasma Version 6.0.3
KDE Frameworks Version 6.1.0
Qt Version : 6.7.0
Kernel version : 6.8.5-arch1-1 (64bit)
Graphics Platform : Wayland

Also writing in to confirm the issue.

Operating System: Arch Linux 
KDE Plasma Version: 6.0.3
KDE Frameworks Version: 6.1.0
Qt Version: 6.7.0
Kernel Version: 6.8.5-arch1-1 (64-bit)
Graphics Platform: X11

Downgrading Solid back to 6.0.0 fixes the issue.

Looking at the change log, there's really only one commit (https://invent.kde.org/frameworks/solid/-/commit/f000b6e99f741c66744a8995f6521e9158ebf289). I think the problem here is that the property "CleartextDevice" returned from the new code defaults to '/' if the device hasn't been unlocked yet, whereas the old code returned an empty string, which clients apparently expect.

Ahh good catch. Should be pretty simple to fix. How can we help the devs? I don't see an option to raise a PR.

Looking at the code some more, it seems that many functions explicitly check for both cases, e.g. in StorageAccess::filePath():

    const QString path = clearTextPath();
    if (path.isEmpty() || path == "/") {
        QString();
    }

Other functions, such as StorageAccess::setup() (which I think might be the culprit here), don't:

    if (m_device->isEncryptedContainer() && clearTextPath().isEmpty()) {
        return requestPassphrase();
    } else {
        return mount();
    }

Perhaps it would make sense to refactor this check into an own function (e.g. StorageAccess::isUnlocked()).

I've assigned the bug to the author of the commit (I hope that's okay to do).

A possibly relevant merge request was started @ https://invent.kde.org/frameworks/solid/-/merge_requests/163

*** Bug 485617 has been marked as a duplicate of this bug. ***

and also in master from yesterday:
Operating System: openSUSE Tumbleweed 20240414
KDE Plasma Version: 6.0.80
KDE Frameworks Version: 6.2.0
Qt Version: 6.7.0
Kernel Version: 6.8.5-1-default (64-bit)
Graphics Platform: Wayland
Processors: 20 × 13th Gen Intel® Core™ i7-13700H
Memory: 62.5 GiB of RAM
Graphics Processor: Mesa Intel® Graphics
Manufacturer: TUXEDO
Product Name: TUXEDO InfinityBook Pro Gen8 (MK1)

*** Bug 485645 has been marked as a duplicate of this bug. ***

This is a polkit issue

I have the same problem

was wrong, downgrading solid fixed it

Also hit Neon User Edition

Operating System: KDE neon 6.0
KDE Plasma Version: 6.0.3
KDE Frameworks Version: 6.1.0
Qt Version: 6.7.0
Kernel Version: 6.5.0-27-generic (64-bit)

Workaround to mount from the cli https://askubuntu.com/a/279218/281142

Git commit 9ecaf388ccd41d2831ab3833c26627f72ab78f40 by Kai Uwe Broulik.
Committed on 17/04/2024 at 10:55.
Pushed by broulik into branch 'master'.

udisks: Return empty string for "root" clearTextPath

There cannot be an empty object path on DBus, so "/" is used to denote
no clear text device. Return empty string explicitly here to avoid
littering even more places with empty || "/" checks.

M  +5    -1    src/solid/devices/backends/udisks2/udisksstorageaccess.cpp

https://invent.kde.org/frameworks/solid/-/commit/9ecaf388ccd41d2831ab3833c26627f72ab78f40

Thanks! Will there be a 6.1.1 release to fix this? I see that Arch already provides a patched version, but many others will likely be affected by this regression, as well.

Git commit a3b18591ba144fae0cd0cfc087a45c64000d4e51 by Nicolas Fella, on behalf of Kai Uwe Broulik.
Committed on 19/04/2024 at 11:03.
Pushed by nicolasfella into branch 'Frameworks/6.1'.

udisks: Return empty string for "root" clearTextPath

There cannot be an empty object path on DBus, so "/" is used to denote
no clear text device. Return empty string explicitly here to avoid
littering even more places with empty || "/" checks.

M  +5    -1    src/solid/devices/backends/udisks2/udisksstorageaccess.cpp

https://invent.kde.org/frameworks/solid/-/commit/a3b18591ba144fae0cd0cfc087a45c64000d4e51

I've found the same bug on Garuda (Arch) with KDE Frameworks 6.1.0.

It happens with all LUKS Encrypted drives which are not mounted, regardless if it's external or internal.
I'm running the OS on a m2 btrfs LUKS Encrypted drive, when I try to access my second m2 encrypted drive connected to the motherboard I get the same error. 

Unencrypted drives mounts OK.

Operating System: Garuda Linux 
KDE Plasma Version: 6.0.3
KDE Frameworks Version: 6.1.0
Qt Version: 6.7.0
Kernel Version: 6.8.5-zen1-1-zen (64-bit)
Graphics Platform: X11

(In reply to tuxx from comment #18)
> I've found the same bug on Garuda (Arch) with KDE Frameworks 6.1.0.
> 
> It happens with all LUKS Encrypted drives which are not mounted, regardless
> if it's external or internal.
> I'm running the OS on a m2 btrfs LUKS Encrypted drive, when I try to access
> my second m2 encrypted drive connected to the motherboard I get the same
> error. 
> 
> Unencrypted drives mounts OK.
> 
> Operating System: Garuda Linux 
> KDE Plasma Version: 6.0.3
> KDE Frameworks Version: 6.1.0
> Qt Version: 6.7.0
> Kernel Version: 6.8.5-zen1-1-zen (64-bit)
> Graphics Platform: X11

it fixes in Garuda with the last update, LUKS decrypts OK.

plasmashell 6.0.4
Qt: 5.15.13
KDE Frameworks: 5.115.0
kf5-config: 1.0

Kernel: 6.8.7-zen1-2-zen arch: x86_64 bits: 64 compiler: gcc
v: 13.2.1
Desktop: KDE Plasma v: 6.0.4 tk: Qt v: N/A wm: kwin_x11 dm: SDDM
Distro: Garuda base: Arch Linux