Backward compatibility is definitely one of the most popular features of PlayStation 5, but we still do not really know how it will work. Is it as simple as running Bloodborne and enjoying it in 8K? No: even if the new hardware is more powerful than the current one, Sony will avoid compatibility problems by captiously studying the ideal performance of each game and enabling improvements where possible.
TwistedVoxel you have found this explanation in an update of the PS5 backward compatibility patent, where the process is illustrated a little better. First, Sony runs each game on its original platform, its performance and records the results. Then, take that same game to the next generation hardware and repeat the process. The objective is to discover in which points both consoles converge and to guarantee that there are no performance problems. If there is a possibility to improve the game in some way with PS5, then it would also take place, but not before.