I use autologin too with disk encryption and i don't see an issue. If you have the encryption password nothing can stop you anyway. And if you put your computer in any sleep mode you have to login after waking up.

it's fine, but I recommend only enabling autologin at boot so you can lock the screen without shutting down the entire PC

You could potentially do it even better the other way around. You can use clevis and tang to have network bound disk encryption setup. That way, anytime you're connected to your network the disk auto decrypts. For laptops, I like to put a decryption key on a USB drive that auto decrypts the drive. Network bound disk encryption doesn't work over wifi and this way I can still have it decrypt on the go but lock it by removing the USB key (like if you leave the laptop in the hotel room just take the USB out and keep it with you).

I'm not familiar with the environment, but depending upon how locked-down the system is and what permissions the auto-logged-in user gets, an attacker could use the session to modify the environment to grab the LUKS password for later collection.

Auto login works on remote sessions too though, right?

I've used this workflow for years and like you said, any attacker would have to know your LUKS passphrase or catch your desktop while the screen is unlocked.