Opening a .set file from a mach3 install on win 11 pops up an error exclamation point, which I believe should also read unrecognized file.  Tried it on one of the screen download from the mach site and got the same error.  If I create a new file and save it, it will  open in screen4 without issue.  Got the same results on a second win 11 machine
Copied the 1024.set file to a thumb drive and tried it on a win10 machine, loaded and edited without issue.

Is this a bug or a win11 issue?

I didn't find this issue on the forum so guessed this was the right spot.

SOLVED.  I had the code loaded in my Mach3 folder but still had the problem.  Clicking on "Default" and setting the Mach Location pointer to the Mach3 folder solved the problem. 
Sidebar, In Windows Explorer, Under Properties of the executable set compatibility to Vista and the top line menu items don't freeze the program.