There is always Tk. It's a very friendly (no sudden unexpected behavior), easy to use toolkit.

https://tkdocs.com/tutorial/index.html

Tk works more or less everywhere and sometimes already installed: https://tkdocs.com/tutorial/install.html

and you don't need to use tcl: https://tkdocs.com/resources/languages.html

If you don't like Python, Ruby, Perl, or Tcl, other bindings are available: https://wiki.tcl-lang.org/page/Languages+with+a+Tk+binding https://en.wikipedia.org/wiki/Tk_%28software%29#Language_bin...

While the stock look-and-feel is functional-but-bland on all platforms, modern Tk is completely customizable and can approximate native widgets: https://tkdocs.com/tutorial/windows.html#dialogs