Ah, okay. In the first post you list all these extensions as being enabled.
I am using an unchanged fedora32 templateVM for my non-networked vault VM.
For other VMs I have template-copies with additional software.
I guess, there aren’t that many differences in our setups.
Qubes 4.1
KeePassXC - Version 2.6.4
Revision: 34a78f0
TemplateVM: Fedora 32 (kernel 5.10.28-1.fc32)
CPU architecture: x86_64
Kernel: linux 5.4.98-1.fc32.qubes.x86_64
Do you have U2F enabled on your Qubes computer? Is this working for you, for example, logging in to the Qubes forum with U2F?
I remember that this problem has been strange for me, as well because I know exactly the problems you are having at the moment.
The database had been corrupted and because I wasn’t able to save it becomes unusable ->> always have 1 or more backups!
Edit:
Did you see this post?
I don’t know about installing such package but maybe it helps?