I'm active in the (hobbyist) field of documenting species. There's thousands upon thousands of websites created by amateurs containing unique niche content. For example, somebody might have made it their lifelong hobby to document every species of bee in their territory.
It's a fragmented mess of incompetently produced websites, but I find it incredibly charming and in the spirit of the original web. Above all, it is their content that has lasting value.
The people behind it are good, generous. That's why it makes me so angry when their work is cast aside like this. Things not just technically breaking, in many cases simply disappearing altogether from search results.
I mean, if I was building a search engine algo, I wouldn't necessarily know how to find the websites you describe, much less optimize for them.
Same for http download links from https websites, will not work anymore.
anything that used cookies on embedded resources will also be broken because of the missing samesite header (same for third party cookies obviously)
if google really goes through with removing alert/prompt/etc from their browser like they said they were planning to a while back, so so many things will break