Manually synchronize Calendar with your online accounts
Open Calendar > Menu > Sync Now.
If you want to get calendar events from an online account on your device immediately, or upload events from your device to the online account (if the account allows it), you can do a manual sync. This synchronizes Calendar with all the accounts you have set up on your device.
Checked against the LuneOS code and installed apps. Nobody has tried these steps by hand yet, so tell us if something differs.