What is now fashionable to write a cross-platform GUI for desktops?

Question

User interface

It took a port of an old already enough application written in WinForms. Everything that I could, I took out into a separate library, which I compiled into .Net Core. Gui left. It is necessary for Windows, Mac and Linux (however, the latter is not necessary).
Maybe someone will advise something, otherwise, apart from Gtk #, something does not come to mind.

Answer 1

Qt.

Answer 2

https://www.mono-project.com/docs/gui/
avaloniaui.net Ignore
fashion.