[pjmlp]

Yes, Windows variants as well.

Microsoft does license Windows to the same OEMs that are having fun with Android, which just like on Android are allowed to do a certain level of customisations.

Windows is not only what comes with a PC.

The only big difference is that AOSP costs zero dollars, euro, yen,.....

[vatueil]

The difference is that it's free and open source. ROMs such as Lineage OS do not need to pay for a commercial license to fork the code, and an app such as F-Droid can run natively on any Android device.