I am not aware of one either.
Same as if using Debian. Unspecific to Whonix. Can be resolved as per Free Support Principle.
For reference:
Insufficient issue description. Rarely anyone will be able to help. related:
Free Support for Kicksecure ™ chapter General Advice in Kicksecure wiki
What doesn’t work?
Note, this is also most unspecific to Whonix.
So no need to wait for this forum here. Documentation, search results and support from flatpak directly should be available too.
Just explore all folders inside that folder and you’ll most likely find it.