You can always just refuse. They will find somebody else for it if they need it (usually they don't, system outages/errors are opportunity cost most of the time, not actual emergencies) but they will most probably still keep you for your normal "day job". I never understood devs who took on-calls without very significant pay bumps. Imagine that in other industries except medical where human life is involved. The market is really not that bad, even now.

I'm about 10 years in doing business software development commercially and I always simply refused.

Software engineer. Normal stuff (k8s, python, aws, postgres, etc)

On-call rotation is not always mandatory, and I always ask in the interview about that.