Android has 75% market share, it's not like you can avoid it, they have practically a monopoly. As much as people like Apple here, it's nowhere near the same market share as Android.
Also you should put quotes around open-source, AOSP does not run on any real device due to a lot of android parts being private + private drivers. It took me one month to run a custom kernel on my Samsung to get the basic hardware working, it's as far as open source as you can get. Android is a "look but don't touch" kind of open-source.
Back in the day Microsoft actually used the existence of Linux as a legal argument that they could not possibly be a monopoly. The judge didn't buy it.
It was mostly Apple and MacOS which were used as the excuse, not Linux. And Microsoft kept both on life support by supporting software for them (e.g. Internet Explorer pre Safari).
You can run Android such as LineageOS without Opengapps perfectly fine. You can also use microG (with or without LineageOS), though that may be against Google ToS.
Also you should put quotes around open-source, AOSP does not run on any real device due to a lot of android parts being private + private drivers. It took me one month to run a custom kernel on my Samsung to get the basic hardware working, it's as far as open source as you can get. Android is a "look but don't touch" kind of open-source.