Hashtags for ProtonDrive files
The ability to add one or multiple hashtags to a file would make organization and searching your files much easier.
For example, if a user has a library of food pictures/recipes, they could search or filter their library for one or multiple tags such as #Vegetarian, #30MinuteMeal, #BBQ, or #Garlic
If Proton Drive offered a searchable comments field for both file folders and individual files, one could then devise their own scheme for quickly finding similar files or organizing them in a way that works best for them using hashtags or whatever. While there would be "zero knowledge of content of files" obviously, there would be knowledge about the comments so that they could be searched quickly and easily. It's just like on Proton Mail where the subject line is easily searchable compared to the content of the email which is typically more secure.