write a cross platform GUI is even more painful. It's pretty much either paying for Qt or use the bloated Electron.js. Looks like the latter won the market. I failed to see other practical options, flutter was an option, but its strength is not on desktop so far.
I personally use it for my desktop apps (cross-platform) and building UI for it is a breeze. Though I forked someone's window styling plugin because it's missing some features I need. A native dev would've done better than me but if it works it works I guess.
If I had to satisfy the requirement in the post though, I'd use enigma protector with to make the app folder into a standalone exe and with compression enabled to make it smaller.