Did it! My old thinkpad x200t is now Windows 10 Pro in S mode
When I first set it up, it was saying not activated, and it couldn't or something. It knew I had a pro license somewhere on the drive. But it said windows 10 s.. Reboots did nothing.... Let it sit around a bit cause I was busy....
Then tried to update store stuff, tried to do windows update... at first it was saying I was up to date, then a few updates appeared, including a culmulative one....
After that reboot and a long update it seemed to finally work! No more activation message and it says Window 10 Pro in S mode.
I did it cause it's the laptop for my parents and kids (while at my parents house)… they complained a lot that it would slow down a lot and get stuck, my 8 year old says glitching... Hopefully this mode stabilizes things for them