Can't open any Thunderbird (flatpak) mail attachements

[macmpi]

What Happened?

I can not open any attachment, whatever attachment setting (System Handler or Always ask).
Thanks for any tip.
flathub/org.mozilla.Thunderbird#182 (comment)

Steps to Reproduce

double-click on PDF attachment: nothing happens
Same with other attachments (RTF, etc...)
Changing default attachment settings in Thunderbird to bring up System handler does not fix the issue: handler does not open Document Viewer, nor would list any other app than Thunderbird itself.

Expected Behavior

PDF document would open with Document Viewer/evince

OS Version

6.x (Odin)

Software Version

Latest release (I have run all updates)

Log Output

elementary 6.1 / flatpak 1.12.4 / Thunderbird 91.6.0 (flatpak)

/usr/lib/x86_64-linux-gnu/xdg-desktop-portal-pantheon --version
0.0 

/usr/libexec/xdg-desktop-portal --version
xdg-desktop-portal 1.7.2

Hardware Info

No response

[macmpi]

xdg-desktop-portal 1.8.1 did not bring any benefit on this issue.
According to this, it would require 1.10.0 at minimum.