Astoria and WSA are different things. Sort of. WSL and WSA both use the approach that was proven by Astoria. That approach was possible since the NT kernel was created, but no one within Microsoft had ever used that feature outside of tiny pieces of experimentation prior to Astoria. Dave Cutler built in subsystem support from the beginning, and the Windows NT kernel itself is a subsystem of the root kernel, if I am remembering a video from Dave Plummer correctly.

Anyway, Astoria was an internal product which management ultimately killed, and some of the technology behind it later became WSL and much later, WSA. WSA's inital supported OS was Windows 11.

Microsoft being Microsoft, they artificially handicapped WSA at the outset by limiting the Android apps it could run to the Amazon App Store, because that's obviously the most popular Android app store where most apps are published. [rolls eyes] I don't think sideloading was possible. [rolls eyes again]

I don't work for Microsoft and I never have; I learned all of this from watching Windows Weekly back when it was happening, and from a few videos by Dave Plummer on YouTube.