All 'adversarial compatibility' from projects like Nitter, Teddit, Invidious, and youtube-dl go out the window. Any archive site (archive.org, archive.ph, etc.) can be blocked by sites requiring attestation.
And just like the book industry was terrified of piracy and were 'rescued' by Kindle, so too will journalism outlets that can't find a business model flock to Google to save them.
This is going to be rough.
What will happen if such a thing actually happens is that the underground market for "trusted device" farms grows, not too different from what's currently already happening but possibly at a far larger scale. Of course, that means the financially motivated scraping services still keep going while the honest individuals wanting user-agent freedom get screwed, just like with many other forms of DRM...
Uhh... Those two matters are pretty much unrelated to each other. Scraping is becoming non-existing because the era of static web pages has ended. No need to "scrap" when you have a nice, performant JSON REST API provided for you.
There are no performant json rest APIs provided these days though. The days of public APIs are long gone.
In practice, if there is a mobile app, there is an API. Whether it's creators object to your usage is mostly their own problem.