Today we’re announcing a new end-to-end encrypted, collaborative document editor that puts your privacy first. Docs in Proton Drive are built on the same privacy and security principles as all our services, starting with end-to-end encryption. Docs let you collaborate in real time, leave comments, add photos, and store your files securely. Best of all, it’s all private — even keystrokes and cursor movements are encrypted.

Literally the second paragraph of the post (but I’m sure you haven’t read it, since you seem so busy replying to every comment here about how Proton is becoming Microsoft or something).