UAC was only an issue for poorly written applications and shabby installation techniques. Least User Access was already a thing long before UAC enforced it, going back at least as far as NT 3.51 days.

You can still run 16-bit "DOS" programs on Windows 10 as long as you don't drink the 64-bit Kool-Aid. QuickBasic, PDS 7.x, and VB-DOS can all be used today though I'm not sure why you'd want to.