I can't change my Monterey user login picture

Hi there - I just got a new Macbook Pro with Monterey (currently running 12.4). I transferred my info from my old MBP and have been using it successfully for a couple of weeks now but one day I restarted and noticed my login picture had changed by itself to a flower.

When I go into System Preferences and try to change it in my Users and Groups setting, there is simply no option to change it and nothing appears in the place it should be.

See screenshot. I tried updating, but no change following my system update. Tried restarting many times, obviously. Any ideas? Thanks!