Android is open source, it is based on a Linux Kernel which has been modified by a variant of C language.
A few years back there was a big controversy when Google banned Huawei due to some security/privacy issues and then you couldn’t use almost any Google services on it.
So if Android is FOSS, then that doesn’t make any sense. Like anyone should be able to use Android on any device they choose, and what stopped Huawei from continuing to use it?