I have a hetzner storage box mounted with sshfs, but I wish I didn’t have to since I’m paying for protondrive too. It took me a whole day to upload my personal files to protondrive through the web interface since it crashed the browser repeatedly and I had to verify what got uploaded or not each time.
Sorry, a “storage box” ìs a product by a company called Hetzner: https://www.hetzner.com/storage/storage-box/
sshfs is a way to mount something remote through ssh so it behaves like a local directory.