Last update: if I go to about:config and set the
layers.acceleration.force-enabled to false the problem is fixed.

I found this: https://support.mozilla.org/en-US/questions/1225327

I tried that and it worked without loading gnome-screensaver. I haven't rebooted, is that needed?

Are you setting transparency anywhere?

For best integration, ideally I'd enforce SDDM when using plasma, but I don't think people would like that.

Hello Sunnyflunk, thank you for looking into this.

Thank you @sunnyflunk, I followed your advice and I was able to auto-login... but in budgie!
To make a persistent plasma auto-login you have also to go into system settings, login screen , advanced, and here configuring the default session.

Not sure of maniphest jargon, but I see that this was accepted for inclusion. Does this means that zerotier package is work in progress?

Hello @folcred , I investigated and I can say that the bugged "battery widged" is, in fact, the system tray.

My battery widget is stuck to "1:57 Remaining" . The % is correct, but the timer never changes.
Not sure when happened but I remember that this used to be ok.