Some mail services do an email import. Proton worked for me.
Here’s what I did and it took time. I started forwarding my email to my new account first. I did a Google takeout of my email in case I really screwed something up. Then I went through and deleted about 2 decades worth of emails I didn’t need or want Google’s AI to access: old newsletters, shipping and old purchase confirmations, emails with contacts that were purely logistical or ephemeral, etc. Going to all mail and searching mail from Amazon or other retailers and selecting all to delete. After that I used proton’s import tool. I went through and updated my email on all my services to my new email account or an alias. I use iCloud and proton pass - while I pay, a limited number aliases are available in the free tier of PP). As my final step I created an Vacation Response for my contacts (of which I edited already) with my new emwil address and told close contacts about the change.
My family already uses iPhones so calendar so it was easy to move to iCloud from Google. Yeah, that’s moving from a lion’s den to shark infested waters, but I do enjoy swimming. /lh There may be other services, but I haven’t looked into them yet. Generally though, you can send event invites to any calendar and even with Proton you can share a calendar, though it’s more rudimentary.
JFC, Claude