unfortunately there is no way to get the game on the other system. This is something I spoke to Al Azif about. Although you can reuse an external hard drive from the PS4 on your PS5 (provided it's the same account, which is a +1 for Sony), you need to log into the system and renew your licenses to play to games, which I don't know if it's automatic or not. There is an option for this in the settings of the PS5 (maybe also the PS4). in fact, with either the latest firmware or the latest beta, you can now download an individual license instead of re-downloading them all. in fact, I was just selected yesterday to participate in beta testing on the PS5, so I have beta 2.0 for 10.0 on my system. it contains things like Adaptive Charging, which for some reason is only available for the PS5 Slim, the licensing I mentioned, and some additional Remote Play features, like limiting which accounts can use it. to use.
edit: by the way, if your other system is hacked, delete the game, then see if the backporters make any requests. To backport a game you need IDA pro or ghidra, and it's too complicated to explain how to use them. it would be like trying to explain code or something.