You're going to find it difficult to export directly to your Proton Drive without using the Proton synchronization software because right now they don't have a publicly published API developer kit. They supposedly have committed to releasing one sometime by the end of this year.
You can check out the open source app called Rclone. It is a cloud drive mounting utility and somewhat supports Proton. It is not tier 1 supported. They consider it tier 4, which is unstable. I would keep an eye on it because Proton is in the process of releasing an API developer kit that Rclone will be able to take advantage of and make their connection to Proton Drive more stable. You can also look for others that might connect to Proton Drive.