It does have to be.

The entire point of consoles is standardized hardware. If it requires a single line of code from the developers anywhere in the process, it doesn’t play PS5 games and you don’t have the library you’re advertising.

The second there’s a single instruction you can’t replicate the same/better clock for clock performance in, it is not a handheld PS5. Especially when anything that doesn’t need the power has a PS4 version.

There’s no chance.

Steam Deck isn’t remotely comparable in performance to a PS5.

PS5 isn’t practical.

Just do a handheld PS4. That’s achievable and opens a huge library.