Typing option+s results in surprise emoji (😮) instead of eszett (ß)

Up until a few days ago typing option+s resulted in the German eszett (ß). Currently typing option+s results in the insertion of the surprise emoji (😮). If I bring up the Keyboard Viewer and press the option key by itself, I can see that in theory at least typing s should insert ß as I would expect. Clicking on the ß character in the Keyboard Viewer also inserts a 😮.

I have tried

• a different keyboard layout which provides option+s as ß: surprise emoji
• activating the standard German keyboard and pressing the key to the left of 0 (zero): ß
• disabling Karabiner, although nothing in the settings suggests such a substitution to be active: surprise emoji

As indicated in an older question, the emoji substitution check doesn’t work on Big Sur.

Do you have any idea how I can debug what is causing this? I cannot recall installing anything recently which might be causing such a change.

I have successfully found out where the replacement was coming from - it turns out there was an entry in ~/Library/KeyBindings/DefaultKeyBinding.dict which mapped option+s to the surprise emoji. I had forgotten putting the entry in there.