On your PC or Mac, go to the Sony PlayStation website. Under "How to update the PS4 console system software," click "PS4 ...

entitled "Initialise PS4 (Reinstall System Software). Selecting this option, the machine then asked for us to insert a USB drive with a fresh PS4 OS on it (which we had already done), so simply ...

For PS4 disks, all you have to do is insert the disk into your PS5, and it will download to your system storage. Of course, this depends on if you have the disc version of PS5 or the digital.