Earlier quoted context omitted.
It's also not some "oopsie". It's almost certainly not news but these sites want these 'one more' behaviors. Years ago, I designed a minimalist YouTube player that removed video suggestions and autoplays but used their player, didn't evade ads, etc. I got banned by Google because they disallow any alternative site for YouTube, only embeds are allowed. Pretty sure I am still banned on all Google APIs too.
You should never expect to have rights to anyone's server API endpoints, esp outside of their TOS, which is basically what trying to build your own front-end independent of youtube.com is. However, with most browsers, you have all the rights to build extensions that hide divs and change styling and add new elements with data that's already loaded (as long as you're not calling API endpoints that aren't called by the…
Thankfully, it's rare because people using ad blockers is apparently rare on the whole.