It would be super-helpful to be able to mark files and folders so that they cannot be synced to other devices (and are therefore only present on the source system as well as at Proton).

This could be useful for sensitive data that exist on the source machine, need to be backed up, but also need to be prevented from inadvertently landing on other (perhaps less trusted) machines.

Implementation is left open here, but could happen in various interesting ways. The most “natural” way I’d see is to navigate to Proton Drive, select a file or folder, then mark it as “sync to Proton Drive only” or some such.