Here’s response (finally) from protonmail.
Per the logs it looked like you're using an older version of Bridge. However, it seems that Bridge stopped working on your side after updating to Bridge 3.19. This is the version where QT 6.8 became a requirement.
You can install Bridge 3.18 from Github and disable automatic updates to ensure it does not update.
https://github.com/ProtonMail/proton-bridge/releases/tag/v3.18.0
If you can, the better option is to update QT to 6.8 or newer which will let you use newer versions of Bridge. However, as a quicker and safer solution at this time, you can use Bridge 3.18.0
First, I installed, 3 days ago, ProtonMail-bridge 3.21 through an rpm from their website. That is what I am currently trying to get running and which does not run. Also, I never did any conscious upgrades from original install . Upgrades must have been done by protonmaii itself.
Secondly, to install qt_6.8 appears, from qt website, to be a compilation that only shows applicability to leap 15.5; not 15.6. This gives me some doubts. It is a very significant compilation.
Third, does leap 16 include qt_6.8 so an upgrade to leap 16 might get past this problem?
thanks, tom kosvic