You are supposed to be able to load custom points of interest onto Garmins from a PC. Here is a full set of instructions, though they may be rather dated.
Rather simpler is loading waypoints. On my old Extrex the name was limited to very few characters, but that was partly because of the very simple screen.
Many applications of GPS technology are now ...
I have a Garmin Oregon, and while it is possible to load gpx files with custom points of interest using the Garmin Basecamp software (https://www.garmin.com/en-US/software/basecamp/), there are a couple of restrictions that make it less than optimal.
the software seems a bit outdated
sometimes it just doesn't work, but you don't get any good error messages
Short answer: yes, and I do this with my Inreach Explorer+. Garmin supports GPX files, among other file types. I have a monthly charge because I wanted the messaging/SOS functionality.
It seems you can do similar with a 65S and Base Camp and no montly charge.
And yes Garmin software is clunky. I have learned to mutter and shake my head.