Thank you for the additional details. This is enough information to work with.
First off, I'm sorry about losing your BD drive pairing. That really, really sucks since it means you will no longer be able to use BD disc with Poopsploit.
So the answer to this one is kind of complex. There is not a tool that lets you merge PS5 backups. However there is a PS5 tool that
should be able to extract your saves from a PS5 backup. Specifically, from an archive.dat file, which is the file a PS5 creates when it backs up the system to a USB drive.
PS5 Bar Tool:
https://github.com/chibsaabji/ps5-bar-tool
The linked copy is a fork that just very recently added support for FW 12.xx. I have not personally used this tool;
not many people have in general, so I cannot offer any guidance on how to specifically use it. But used in conjunction with Garlic, in theory this should allow you to get your saves out of the backup, and then put back into your PS5 via Garlic.
The other thing that comes to mind is using
Netflix-N-Hack as your initial userland exploit, rather than Y2JB. That could allow you to restore your backup, and then Netflix-N-Hack your way into an initial jailbreak, from which you could install YouTube for Y2JB. However that method has somewhat finicky rules about an activated PS5, and I'm not sure your restored-from-backup system would meet them (someone else here may know more). Still, it may be worth a shot.
As an aside:
Jailbreak with P2JB/Y2JB/poopsploit (not sure which is which but the 50 minutes long jailbreak)
Y2JB is the name of the YouTube-based userland exploit to initially get into the system.
P2JB is the name of the use-after-free exploit in the PS5 OS kernel that can be used to gain kernel access; this is the one that takes 50 minutes.
Poopsploit is a different use-after-free kernel exploit that is fast, but it can only be used from a BD disc, which is why it can't be used in conjunction with Y2JB.
