I recognize this will vary depending on how much you self-host, so I’m curious about the range of experiences from the few self-hosted things to the many self-hosted things.
Also how might you compare it to other maintenance of your other online systems (e.g. personal computer/phone/etc.)?
Depends what are you doing. Something like keep base os patched is pretty much nil efforts. Some apps more problematic than others. Home Assistant is always a pain to upgrade and something like postfix is requires nearly 0 maintenance.