I built a Tcl/TK GUI in 1997 and I thought that it (specifically Tcl) was dated then. If you're used to anything beyond shell scripting, Tcl feels very un-programming. It does look they added objects in 2012, I can't speak to that.

Notwithstanding anything about LLM tools being able to do GUIs any way you want in 2026, I'd really consider just about anything else at this point. JavaFX, React Native, Electron, Flutter, etc.