avidamoeba@lemmy.caI was in the same boat until recently. Got a Proton account. There’s trivial import setup that both grabs all your email from Gmail, and it sets up forwarding.
Then you gotta start changing your email in different services to the new one. Should probably register domain for your new email so that you don’t have to do this exercise again if you switch out of Proton.
Install Proton’s mail bridge and Thunderbird to backup all your mail. Has better search too.
Painfully migrate all accounts to the new email.
For existing emails: IMAP the old gmail, export them somehow and reimport to the new account.
For new that still arrive on gmail: Auto forward