It’s not that it’s closed, it’s more that none of the exiting email protocols support a server which can’t read your email (as it’s all encrypted). They do offer Proton Bridge which you can run locally which will handle all the decryption and local mail clients can talk to that as the would any other mail server.
I don’t know off hand if it supports calendar syncing though.
FYI for anyone interested. Immich is a open source, self hosted system for photos/videos like Google Photos. It uses machine learning locally for facial and general image recognition.
I’ve used it quite a bit recently. It makes it really easy to submit data in small amounts. I usually have it open while walking my dog and enter in basic things as I go. I’ve completed about 1500 quests so far with it.
This was the tool I used. It worked great for me.
Set Immich up a couple weeks ago and I’m surprised how good it is. Their docs included a simple cli tool to bulk import all my Google photos. Mobile app is working great. I’m really impressed with the search too.
The reason that Google got ruled against originally was that they were paying and offering incentives to developers to keep them from releasing their apps on other app stores.
Google also doesn’t support a user installing the Play Store themselves (and the required Google Play Services dependency). So phone manufactures have to choose to include it on everybody’s phone from the get go, or their users won’t be able to use it at all.