Not too bad to fix
So, I'm not a big fan of rolling out breaking changes on release (ala Chrome); rolling it out in a Beta is fine.
But independent of that... sites this does break, at least they don't really need to "fix" the site (some redesign, moving bits to different domains or whatever, so the cookie use is "Lax" at least); they should, but at least they can just put the "SameSite: none" or the like into the headers.