Hi there,
I think I found a more precise/surgical solution for this problem.
Thanks to @schmidty suggestion I opened my %localappdata%\Docker folder and found some log files;
The most recent reported
[GoBackendProcess ][Error ] msg="unable to parse C:\\Users\\...\\AppData\\Roaming\\Docker\\settings.json: while parsing JSON from C:\\Users\\...\\AppData\\Roaming\\Docker\\settings.json: invalid character '\\x00' looking for beginning of value"
In fact %appdata%\Docker\settings.json was unreadable!
It was enough to delete that file to make docker desktop start again.