There are at least two GUI toolkits that run on TeaVM: 1. Codename One. Similar to swing, but focused on mobile https://www.codenameone.com 2. SnapKit. Targeted at desktop. Also a light-weight toolkit, like Swing. https://github.com/reportmill/SnapKit
It could work though by drawing to canvas.
That's what Avalonia does in C#: https://avaloniaui.net/
Here's a clone of Visual Basic 6 written with Avalonia and compiled to WebAssembly:
https://bandysc.github.io/AvaloniaVisualBasic6/
https://github.com/BAndysc/AvaloniaVisualBasic6
There are at least two GUI toolkits that run on TeaVM: 1. Codename One. Similar to swing, but focused on mobile https://www.codenameone.com 2. SnapKit. Targeted at desktop. Also a light-weight toolkit, like Swing. https://github.com/reportmill/SnapKit