A 1992 CD player is the oldest GUI app that still runs on Windows 11
Oldest GUI application that still runs on Windows 11
Windows 11 can't run 16-bit software, so the hunt for the oldest unmodified GUI app lands in the early NT era. A 1993 FREECELL.EXE from Win32s works fine, but the author digs deeper and finds CDPLAYER.EXE from NT build 347, linked in November 1992, which runs because it relies on crtdll.dll still shipped in SysWOW64. With a small emulation DLL, it even plays audio. Cheating with otvdm gets REVERSI.EXE from Windows 1.01 (1985) running too.
At the time of this post, that's a 33 years and 8 months old application, which is impressively almost as old as me.