iCloud not sending Calendar alerts

I open Calendar on my Mac (Apple M2 Pro, macOS 15.6.1) and Alerts always resets to "Account: On My Mac." I want all alerts to come from "Account: iCloud." I set it to iCloud, quit Calendar, open Calendar, and it's back to Account: On My Mac. I set Calendar Alerts back to iCloud, quit Calendar, reboot, open Calendar, and it's back to Account: On My Mac, and no events are available to Calendar. In other words:

I set Calendar Settings to this panel:

But my Mac always resets to this, not what I want. Checking the box for "...alerts on only this computer" has no effect.

Any suggestions or recommendations are welcome.