Everyone on the internet is free to go and use any other service.
Yes but that's not the claim you made. You wrote "It’s their private website, they do on it whatever they want. Right, lemmy?" and this blanket statement is wrong. They can't to "whatever they want" because they are bound by laws. If Google/Alphabet instituted rules on YouTube that competing video services like Nebula cannot named at all, market watchdogs would be at their heels immediately and they'd win in court if it came to it.
Can they put ads on pause screens? Yes. Can they do "whatever they want"? No.
Interesting how the numbers between "computer pros" and hobbyists (Steam Survey) diverge. Unsurprisingly for Steam gamers the Windows numbers are way higher but for Linux specifically Ubuntu is crashing hard since a few years from absolute domination to all Ubuntu versions + derivatives (Mint + pop_OS) combined barely making up 20% of the Linux user base whereas at Stack Overflow there's a clear lead of Ubuntu over the rest.