Bug #6463 seems still to be a thing.
On 2.7.6 flatpak and the fields are still not cleared … at least with SQuirreL and on web server logins.

KeePassXC - Version 2.7.6
Revision: dd21def
Distribution: Flatpak

Qt 5.15.10
Debugging mode is disabled.

Operating system: KDE Flatpak runtime
CPU architecture: x86_64
Kernel: linux 6.2.0-36-generic

Operating System: Linux (Ubuntu 22.04)
Desktop Env: Gnome resp. KDE from Flatpak runtime
Windowing System: X11

Linux ******* 6.2.0-36-generic #37~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Mon Oct 9 15:34:04 UTC 2 x86_64 x86_64 x86_64 GNU/Linux

PS: didn’t expect such problems with a KeePass2-to-KeePassXC transition. :-(