PlayStation crossbuy is great, I used it for many games.As a guess I would be pretty surprised if you had to purchase TLoU2 or GoT or other Sony PS5 titles separately from their PS4 SKUs, but that will be Sony's business decision. The technical capacity is there for any publisher that wants to use it.
If I'm not mistaken, Cross-buy has so far worked only with digital purchases, but that was the consequence of PS4 not having the ability to load discs from old consoles. Many digital games were offered as PS3-PS4-Vita crossbuys.
But now, PS5 can also read PS4 discs. Sony needs to confirm if those old disc games will get a license for a download of PS5 version. Will PS4 games be able to be automatically patched for full PS5 use?