I just had to edit a Google Doc for a university thing, and I found the mobile UI to be rather nice. The desktop UI, too, was very good, and I remember having good experiences with Google Slides before I began my privacy journey.
I am fully capable of using things like LibreOffice and ONLYOFFICE, and I currently just use Markdown and CSV for my documents and spreadsheets.
However, if there’s a FOSS and privacy respecting piece of software out there with a similar UI/UX to Google Docs/Slides/Sheets, I would would be very happy to hear about it.
For the docs part, Proton has an alternative built into Proton Drive that is directly aimed at Google Docs. I can also recommend Cryptee, which can work fully offline and is completely web-based.