Here are the key lines:
On Compatibility:
1.Sony has told PlayStation 4 game developers that any new titles submitted for certification must also be compatible with PlayStation 5, beginning 13th July
2. A game will be deemed compatible with PlayStation 5 only if its submission code runs without issues on Sony's next-gen machine, and provides the same features on PS5 as it does on PS4
On Patches:
1. If a game was originally submitted to Sony after 13th July 2020, any future patch or remaster to that game would need to keep PS5 compatibility. Once a game is PS5 compatible, it must stay so.
2. If a game was originally submitted to Sony before 13th July 2020, any new patch or remaster after that date would not require PS5 compatibility, but it would be "strongly recommended".
So we have several things going here. If a game is submitted after July 13, it has to work on the PS5. Full stop. Compatibility only means that you are getting the same experience on the PS5 as you would on the PS4, no better no worse.
If you need to patch your game and the game was submitted after July 13, the game has to stay PS5 compatible. If you need to patch or remaster your game and it was submitted before July 13, it does not have to be PS5 compatible but Sony strongly recommends it.
What is the ramifications of this. Honestly I don't know.