Unfortunately, the Proton Drive Android app is pretty useless.

It's essential that you can also edit files with it.
When a file is opened (e.g., DOCX, XLSX, ODT, ODS, etc.), a suitable installed app should open to view and edit the file. When a change is saved, it should then be synchronized with Drive.

This is how Google Drive and Nextcloud do it. I'm actually shocked that this doesn't work with ProtonDrive.