No serious problems to report, but I thought it might be worth documenting the few wrinkles I had to sort out in case it may help others.
The Korg drivers were screwed up, as usual. Korg drivers still have to be in the first 10 Windows driver slots. Sigh... Good grief, Korg! What year is this? Seriously?!?! I did the usual fiddling around to bodge a solution on Korg's behalf...

...which resulted in my audio interface not being found on next start-up of Cubase, so I had the job of re-building all my I/O settings. Tiresome, but it worked.
My eLicenser needed updating. No problem there.
My pair of MOTU MIDI Express 128 interfaces yet again decided to swap themselves around... and then swapped back on next re-start. They haven't done this for a few years. I long ago learned to keep two versions of my Cubase MIDI Devices file - one 'normal' and one 'reversed'.
Now I will come to the Win 11 feature that has me concerned for the sanity of the Microsoft development team... Who decided on the right-click 'Show more options'! How did *anyone* think this was good idea?! Cut, copy, paste... all of those use-all-the-time context menus are all now hidden behind an extra mouse click. Utter stupidity!

Happily I know of a registry hack (And Win Aero Tweaker) to solve this. Would that the Microsoft analyst who dreamed this one one up could be fixed so easily...
And that's about it. An hour or so of mopping up, but all is well. That's the last of my PCs brought bang up to date and it's been relatively painless.