My bad, I wasn't being clear. Firefox now supports passkeys, but afaik doesn't have a service for it. So you can use e.g. Bitwarden in Firefox, with Bitwarden storing the passkey, and Firefox just "handing it over".
I've had however a couple of sites that refused to create passkeys in Firefox for my Bitwarden, but that seems to be site specific.
Glad you found a better solution. At home, I scan every letter I get, getting me to 99% paperless. Imagine my shock, when I doscovered that Gnome's "Simple Scan" took sharper scans at one tenth the filesize than "HP Smart Print".... on my HP printer. No login bullshit, no "oh, we analyze your scan for content to suggest a file name", no nothing. Just the possibility to click a button, and get a great looking pdf at a ver decent file size.