Desktop app on Linux does not respect default browser selection

[pappasadrian]

• This is not a feature request (existing functionality does not work, not missing functionality).
  I will request features on forum or via support.
• I've searched and did not find a similar issue.

Describe the bug
When clicking on any link in an email, the site is not opened with the default browser (firefox in my case), but with a different installed browser (chromium). All other apps respect the default browser selection, which leads me to think that this is an issue on tuta's side (or maybe something to do with appimage?)
This is a somewhat recent behaviour, it used to work properly I think until a couple of months ago? Can't remember for sure.

To Reproduce
Steps to reproduce the behavior:

1. Click on a link in any mail
2. Instead of opening with the default browser, link opens with chromium

Expected behavior
Tuta desktop opens links with the default browser (as defined in system settings)

Desktop (please complete the following information):

• OS: Ubuntu 24.04
• Gnome
• v232.240626.0