Apple has NO OEM. You can only buy completely integrated products period. The new M1s are SOCs, so there isn't even a 3rd party market unless you restrict that to USB and fashion accessories.

Microsoft does make its own hardware. The Surface line of products are pretty amazing. They didn't break any OEM 3rd party market nor dictate anything. In fact, they have a "signature system" policy for their first party hardware that it won't be full of bloatware like 3rd party OEMs used to do.

Google has slowly been destroying its 3rd parties and 3rd parties playing in its ecosystem have been moving towards forking for a while which is why there is always the complaint of unsupported devices after a single cycle there. (and so many community roms/hacks/installers floating around to address this)