I have about 6 years of events in my Google Calendar, including a lot of client meetings I might need to look up later. I want an offline copy in case the account gets locked or something. Is there a way to download the entire calendar as a file?

Yes, Google gives you an ICS export.

1. Open calendar.google.com on a computer (the phone app does not have this).
2. Click the gear icon, then Settings.
3. On the left choose "Import & export", then Export.
4. A zip file downloads. Inside there is one .ics file per calendar.

Unzip it and keep the .ics files somewhere safe. ICS is a standard format so you can import it into Outlook, Apple Calendar or another Google account later.

Two small things. Calendars that only show up because someone shared them with you may or may not be in the zip, so open it and check. And holiday or subscribed calendars are not worth backing up because they come back automatically.

Got the zip, there are 3 files, one for my main calendar and two others. Does the export include attachments and the video call links?

The meeting link text is inside the event description or location field, so it is saved as text. Attachments on events are stored as links to the file in Drive, not the file itself, so make a backup of the Drive files separately if they matter.

If you want a belt and braces option, Google Takeout also has a Calendar option that gives the same ICS files, and you can schedule it to repeat every 2 months for a year.

Perfect, that is what I needed. Backed up and I also scheduled the Takeout. Thanks!