With a growing subset of YouTube’s users becoming more aware of how the platform is monetized, YouTube appears to be paying greater attention to those with a preference to opt out, whether that’s through browser extensions like uBlock Origin or other methods that require even less effort.
Unlike with Reddit, this was already clearly and obviously against terms of service.
IIRC, you can make an alternative front end to YouTube, but it has to include the video ads. Somewhat ironically, many of those aren’t even from YouTube themselves, but especially on videos with music, they’re assigned by the RIAA to cover licensing costs.
If Reddit had done what YouTube does and just added a requirement for apps to display the sponsored posts, there would certainly be some mildly annoyed users, but it would not have come to the current level.
That’s only if you agree to the developer TOS. Invidious doesn’t use the Developer API and as such never agreed to the associated TOS. This is against a terms of service that is not relevant to Invidious.