I just plugged the steam deck in to a monitor and while I was transferring some roms and started to wonder if it would be feasible to use as a day to day computer while docked.
I use it as my only personal (i.e. not work or shared) machine, and it is absolutely great. I expected to be installing a 'proper' linux distro on an external drive for the docked use-case, and it has turned out to be completely unnecessary. For those things not available as flatpak, distrobox/podman has been great. (The only thing that slightly irks me that is missing is support for a printing service, but I haven't tried that hard to fiddle with that, since I can do it from my phone on those rare occasions I need to.)
It is, though for a fully fledged Desktop experience you should wipe SteamOS and install an actual desktop distribution.