Are you sure you turned off password authentication? Did you also set UsePAM to no?

Might help if you posted your sshd config as well as provide what error message you get when trying to connect via ssh.

I just tested on my deck and it works for me.

I made the .ssh directory.
I have a single file in that directory called authorized_keys
The contents of that authorized_keys file is the contents of my id_ed25519.pub file from the server I'm sshing from. (id_rsa.pub should work too)

I made no other changes to ssh on the deck.

These are the permissions on the dir and files:

(deck@steamdeck ~)$ ls -l .ssh
total 4
-rw-r--r-- 1 deck deck 96 Aug 23 15:32 authorized_keys
(deck@steamdeck ~)$ ls -ld .ssh
drwxr-xr-x 2 deck deck 4096 Aug 23 15:32 .ssh

Yeah... with your reply, I've tested ssh from FreeBSD --- that works, but putty does not. Not sure why putty does not. Seems specific to the deck, too --- as I typically have dozens of putty open at any time on my workstation ... but only the deck is busting my but for a password.

... and it's not username --- as I'm logging in as all kinds of different users (I wear many hats). Very odd.

Interesting the coming from putty to the deck (password). ssh-add -L works. Then ssh to another host (FreeBSD, linux) works. The keys are there.

I haven't set up putty for shared key auth in many years. I assume there is an issue with that somehow.

Even with password auth enabled, it doesn't prompt me for a password if I succeed with my key.

If I fail when entering my key passphrase it will prompt me for a password though.

You could do a test by copying the id_rsa and id_rsa.pub files to your deck in the .ssh directory and attempting to ssh to localhost.

Be sure to set the proper permissions on the files. (and remove them after the test so they don't end up falling into the wrong hands easily)

That's how it works for me. putty just uses an auth daemon --- I use KeePass ... just because ... but if the key fails, it asks for a password (on other hosts)... but the keys work.

Even on linux (I use FreeBSD mostly). But I have half a dozen pis around ... running linux. No problem with keys. Only the deck.

Try sshing from one of those other linux devices to the deck, to eliminate putty as a variable

I did... and it works... but still it's deck vs. putty, not putty alone.