WebAssembly is supported as a target in Qt 5.15, but skipped in Qt 6.0. Intent is to bring back the WebAssembly support in Qt 6.2 as Technology Preview (TP).
Full WebAssembly backlog here: https://bugreports.qt.io/secure/RapidBoard.jspa?rapidView=258
The following high level functionality is required for pure UI related aspects:
- Qt Gui
- Qt Declarative
- Qt Quick