The push notifications would be a issue for me. I am using GrapheneOS without any google services.
Also the calendar i am not 100% sure how I want to do it. I currently use Nextcloud and Caldav. Which for me works great when syncing with Etar on my phone and Evolution mail in the desktop. For my dad I have setup caldavsynchronizer for outlook as that is the email client he has used for years. When i would use Tuta id loose the nextcloud calendar because it can in no way synchronize with Tuta. With proton on the other hand I can use the bride for email and use the calendar how i am currently using it together with Etar on the phone.
On the other hand if say Tuta providers a calendar that is integrated and works with both the email client on the desktop and on the phone. the same goal is accomplished.