I don't recall having tweaked any setting to have "udiskctl mount" working without password in the same exact situation, but whatever happened, after the upgrade from Debian 10 to 11, it no longer worked.
While there are quite a few examples of how to set up the correct "polkit" rule for it around, most of them refer to a newer version of polkit that uses a different syntax. Debian's pkaction version is still 1.105. And apparently the file needs to be in the correct...