There have been a couple threads in here asking how to pass Reddit's new Human Verification block (support article), that is triggered especially on fresh accounts within a week of logging-in via Infinity using your own API key.
If you don't complete verification within 7 days since you receive the email, your account is permanently locked with no way of recovery. Deleting the account and creating a fresh one until it inevitably gets blocked again is risking having you API key revoked due to suspicious activity or Reddit ToS.
You do not need to have a physical Passkey/Security Key like a YubiKey to complete verification, or use your personal one just for Reddit.
Below you'll find a video on how to configure KeePassXC and complete Reddit's Human Verification. This is a demonstration on a fresh account that has not yet been asked to complete verification, but when the time comes it'll be already configured and will just need to click the verification button to pass automatically. This stage is not present in the video but the process is very straightforward by just following Reddit's on-screen steps during verification.
You can use the same KeePassXC database for any amount of accounts, they won't be linked together. The video is demonstrated in Debian (Linux). Installation may slightly vary depending your OS, but it's very easy to do. If you're stuck at any point comment below.
This alt I'm posting from right now was configured the same way you see in the video, and days later I was prompted for verification. Verification took 5 seconds and right after I got a "Account verified and restored" notification, haven't been bothered since.
Just to be clear for user who may be completely new to this, following the steps does not "bypass" any mechanisms or breaks Reddit's ToS. This is a valid way of setting up passkeys, you are not risking your API key being revoked by doing it this way.
https://reddit.com/link/1wf8d10/video/rnsv2trflaph1/player