You can be in control of your actual data pretty easily with gmail. One of the better options I’ve found for maintaining a local archive is the Got Your Back[0] script. It maintains an SQLite DB with all of the message tag associations, and stores all your emails in standard .msg format text files.

If you want additional peace of mind, you can spend a few pennies and use restic[1] to do regular incremental backups of the archive to Backblaze B2 to add yet another storage location and version index.

[0] https://github.com/jay0lee/got-your-back/wiki

[1] https://restic.net