Other drives like Onedrive and Google Drive give the option to use the smartphone's own office apps to open documents, spreadsheets, slides, etc...
I really miss that as I cannot open my sheets, for example, unless I download them. And if I make a change in them, then I have to upload it to the Proton Drive afterwards.
Sorry, but just to be clear. In those other drives like Onedrive, you do not need to download the sheet in other to open it and if you edit the sheet, then Onedrive automatically replace the older version as you save the edited sheet.
If you implement this, it would also release the pressure on the enhancement of Proton Docs, as users could just use some other office in their phone like Word and Libreoffice as you work more on Proton Docs and (I hope) Proton Sheets.