Just picked up Morrowind from the sale. Fresh install on Win10. Very excited. And then ... Morrowind freezes at launch.

I've tried the usual culprits (run as admin, set XP compatibility) but to no avail. This being from GOG I assume any DRM checking will have been addressed, so I'm at a bit of a lose what to do next. Is there a "definitive" checklist of what to do? Or any ideas what the issue could likely be?

Sounds very odd to me. Did you change anything on the launch screen (options, data files, ...)? Or are you using any mods? Anything else except installing the game?
If not, then it might be a corrupted file, a CODEC incompatibility, or something similar.
How are you launching the game? Desktop icon? Explorer link? Morrowind.exe directly? You might try all 3 methods.
Try un- and re-installing the game, possibly after redownloading the setup file - uninstalling means uninstalling, not deleting the game folder.
How do you get out of the freeze? Reboot PC, cancel task via task manager? Anything else?
If you are using Galaxy, then there might be an incompatibility of Morrowind and Galaxy (I'm not using Galaxy). In this case you might try the non-Galaxy download.
Good luck!