The AOSP is based on a modified version of the Linux kernel, so it is a Linux in that sense, but using it is quite different from using more traditional GNU/Linux distributions.

From what I take from the OSes listed in the sidebar of this community, this place is intended for linux-based phones which are not Android. There are already communities which are focused on Android/GrapheneOS/LineageOS, so it’d be fairer for this one to focus on the rest.