When the RPi 3 was the current model, I used it as a desktop machine for about 2 months. Not exclusively but as much as I could. That was the first quad core, with 1GB RAM. Nowadays you have 4GB and even 8GB RPi 4 options with a somewhat faster processor.
With a 1080p TV as a monitor it was very usable but only if you replaced the built-in web browser with Chromium. It wouldn't do 1440p. I posted here a number of times from it. I remember YT videos being what broke the usability and why I gave up using it though it's entirely possible that performance detail (and 1440p support) has been worked out.
I used LibreOffice which worked fine but I don't even use MS Office much for work even though I have a license for it.
I think for day to day use it would be fine for many people especially with 4GB as I never came close to using all my 1GB, but it really was mostly a media consumption device for me.
Edit: What I liked the most about it was the active way you used the OS for manually installing and updating things from the command line and needing to configure the occasional thing from a config file. There was more old-skool computing feel to it, the direct opposite of how phones work and where the macOS is slowly heading.
Edited 1 time(s). Last edit at 12/21/2020 02:44PM by Lew Zealand.