No there's no public available API and AFAIK there are no plans for that.
Proton
Empowering you to choose a better internet where privacy is the default. Protect yourself online with Proton Mail, Proton VPN, Proton Calendar, Proton Drive. Proton Pass and SimpleLogin.
Proton Mail is the world's largest secure email provider. Swiss, end-to-end encrypted, private, and free.
Proton VPN is the world’s only open-source, publicly audited, unlimited and free VPN. Swiss-based, no-ads, and no-logs.
Proton Calendar is the world's first end-to-end encrypted calendar that allows you to keep your life private.
Proton Drive is a free end-to-end encrypted cloud storage that allows you to securely backup and share your files. It's open source, publicly audited, and Swiss-based.
Proton Pass Proton Pass is a free and open-source password manager which brings a higher level of security with rigorous end-to-end encryption of all data (including usernames, URLs, notes, and more) and email alias support.
SimpleLogin lets you send and receive emails anonymously via easily-generated unique email aliases.
Thank you for letting me know!
Official API client used by proton: https://github.com/ProtonMail/go-proton-api
I didn't see any good documentation. Its in use by (or has at least inspired) https://github.com/henrybear327/Proton-API-Bridge?tab=readme-ov-file
The API bridge backs rclone's Proton Drive support.
What's caldav and carddav used for?
Usually sync calendar and contacts.
Proto calendar does have an ics thing. Maybe you can use drive to backup your contacts
Not there. But would be great. At least a way to backup and recover your contacts to a new phone (both Android and iOS). That would be awesome.