Good news: "Ubuntu on Xorg" does the job.
I had already uninstalled nvdia-driver-470 in order to use my digital signature
application (which does not work with them).
So I've simply started a new session, logged in with "Ubuntu on Xorg": now
weather widgets works as they are supposed to do (as yo
** Changed in: mutter (Ubuntu)
Status: Incomplete => New
** Summary changed:
- Weather widgets appear in the wrong position in a Wayland session
+ my-weather-indicator widgets appear in the wrong position in a Wayland session
** Changed in: mutter (Ubuntu)
Importance: Undecided => Low