I agree with you on principal and don’t mean to sound dismissive but they’re all doing this already.
When I’m trying to look at anything on Twitter it shortly launches a full screen thing demanding I login (I refuse to sign up).
YouTube requires sign-in for age restricted content.
Google, most annoyingly, makes me complete several captchas for using incognito+private relay
Instagram won’t open in safari with incognito+private relay; I have a throwaway account for just looking at the odd link someone sends me in a meme group-chat; I have to use another browser.
I often have to replace “www.whatever.reddit” to “old.reddit” on my phone to be able to see an “age restricted” post, most of the time they aren’t anything a kid shouldn’t be see either, not sure how they’re determining that.