Proton Drive client for macOS is on beta right now.

We’re also beginning the beta for our upcoming macOS desktop app for Proton Drive. As with the other Proton betas, we’re starting with Proton Lifetime accounts today, with Visionary users to be invited later. While community feedback is always important, it’s especially vital at these early stages, so we will send beta invites via email based on our ability to keep up with the feedback. We’ll collect feedback both on Reddit and at drive@proton.me. Once the macOS app is released, we’ll also work on our planned Linux version.

https://proton.me/blog/proton-drive-windows