It's possible to natively integrate your Google calendars with Thunderbird 102.* . However, it's not possible to open a shared Google calendar, you're only presented with your own calendars to open. Adding via the calendard URL doesn't work.
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@schnuffitoI think you can get this feature with the "Provider for Google Calendar" plug-in for Thunderbird.
HOWEVER, there are some caveats! I have had difficulties accepting/rejecting meeting requests, dismissing reminders, synchronizing, etc. with the "Provider..." plug-in. So much so that I have had to make my Google Calendars read-only in Thunderbird.
Native Thunderbird support for (OAuth) Google Calendar is great and doesn't have those issues, but the lack of support for shared-with-me Google Calendars means we're stuck with the Google web interface for now.
If only this useful idea could get the same attention as, say, support for certain icon themes...