An idea.. imagine putting SSO stuff into a Container and setting First Party Isolation off for just that Container.
ive had it disabled for years and never had any kind of issue with single signon websites
knowing what fb is doing with your data, why would you still want SSO?
Because it doesn't have a way to break only FB SSO. All SSO would break by default.
I mean it's too late now but there's nothing fundamental about the current SSO design. If browsers shipped with FPI from the beginning SSO would still work, it would just look different.