Windows 10 user here as well. Just finished playing through a heavily modded Fallout 4 and wanted to do the same with Skyrim. I installed Skyrim Special Edition via Steam, ran it once, and closed the game before loading up Nexus Mod Manager to start modding the game... and of course Nexus Mod Manager can't find the game even when I point it to the exact folder containing the game's EXE. I guess I was just never meant to play this game. Edit: Actually, it looks like a workaround can be managed by just manually downloading each mod and thereafter manually adding each mod to NMM. It's a lot of extra clicking (especially if you want to maintain the mods into their respective Nexus categories which you have to manually reassign for a lot of them), but it seems to work.