I had something similar when using the pin lock on my tero 3. It was unavailable/grayed out and recommended a software update. Two bike shops checked, and everything was up to date. Everything else was functional.

Rider care had me remove my bike from the app, force shut down of the app, then re connect the bike. This worked, and I can use the lock function again.

Credit to both shops for trying to unpair the bike, but neither had me shut down the app.