I used App Manager (io.github.muntashirakon.AppManager) for the screenshot; you can use your regular 'Installed Apps'/'Apps' menu to see if it's been rolled out automatically for you as well.
edit: First link was originally a typo, my bad. Fixed it.
Easier said than done, especially as there are more models that don't have any sort of support for those OSs than models that do. Not to mention the hassle to even enable the option to flash it and risk of bricking. Worse, banking apps may refuse to work.
Google and the OEMs never wanted you to own your phone and they are mostly winning on that front.