Apple - I can't see Google Calendar on macOS Calendar app

You need to tick the calendar in your synchronization settings.

Did you try to move your cursor over the "Google" label (shown in your screenshot) to check if you did not accidentally tap the "hide" button which only appears in this situation? There should be a "show" option appearing if your Google account is functional.

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Edit:

If previous didn’t work try to quit Calendar and to delete device caches:

• In Finder click on the "Go" menu, hold alt and tap "Library"
• Go to "Caches" and remove all folders

Then remove Calendar data:

• While still in "Library" folder remove all files and folders in "Calendar"

Be sure to backup this last folder before doing anything as it contains your personal data. Launch Calendar app and see if it worked, if not do not forget to refill Calendar data with your backup.

This is a pretty bad problem that Apple hasn't fixed yet. You need to delete the calendar cache, see here on how to do that.

This worked for me.