You were right. Even in the Modded Warfare video there was a comment below that the account activation is needed.. I decided to just do it with the backup file and now everything is working flawlessly.
So, I did the JB long time ago when it just got out, I've put the console in the closed and never turned it on until now. What I did is that I followed the Modded Warfare's guide " Jailbreaking the PS5 with Y2JB (No Backup Required)" but I...