can QEMU fake an android environment in a desktop ? Can QEMU be used to fake windows, Linux and Android together ?

Virtualization doesn't "fake" anything, it virtualizes.

And a quick search reveals there are multiple ways to virtualize or run an emulation layer on Linux and Windows for different things (e.g. Wine and WSL).

I'm not particularly familiar with QEMU, but yes. It is possible to get Windows, Linux and Android apps running side by side, with a good set of emulators.

As with all emulation:

• It might or might not be fast.
• Some apps may not work entirely correctly.

Looks like it was possible with android x86 but the project was discontinued.

I just found this it seems interesting.

https://www.intel.com/content/www/us/en/developer/topic-technology/open/celadon/overview.html

The common way to run android apps on Linux is Waydroid. https://github.com/waydroid/waydroid

It seems you are looking for:

• Waydroid or Anbox for android apps
• steam/proton/wine and winapps for windows
• linux for linux. :D (to be completelt serious: distrobox, toolbox, flatpack, docker for apps thare might not be packaged for your spexific distros)

Some are just translation layers (eg. Wine) which usually are way faster but have worse support than complete virtualization (eg. winapps).

But all those project should give you the same experience as running all apps natively in linux.

Fake?

BlueStacks for windows is an android emulator that's pretty good.