That Linux kernel is full of Google specifics, uses a microkernel like architecture since Project Treble, can be compiled since years with clang, now uses Rust for Bluetooth drivers,...
"The timeline for shifting to an "upstream first" cycle for new features starts in 2023, with 2020-2022 dedicated to making it work for pre-existing functionality. The Pixel 6 is expected to be the first Android device to ship with the GKI and Linux kernel 5.10, marking a major step in this process."
Means this is still one year away, if it actually happens, and then only Pixel devices will support it anyway, as so far most OEMs couldn't care less.
Not to mention that upstream will never accept all the things that make Android Linux not really Linux.
Most embedded/embedded-like devices running Linux are running a modified version of the kernel with a heavily customized userspace. These are still Linux by any reasonable definition. I'll leave it at this.