How do you use your YubiKeys?

I'm a little late on this, admittedly. $dayjob is requiring us all to set up a pair of YubiKeys, and I'm using them for the first time and my mind is a little blown.

I was seeing articles about "passkeys" all summer, not really grokking what they were talking about, clinging to my usernames and passwords and 2FA codes coming out of 1Password, etc.

I just set it up on a few accounts today, initially as an additional 2FA source, but when I set them on GitHub, I saw for the first time how exactly they are used instead of the username and password and 2FA combo to log in, and it seems incredible to me!

For long-time YubiKey users: what are some cool things in the ecosystem that you would recommend looking at?