I had this issue for a long time since Launch. Once I redeemed the codes, they never installed and neither could I find them on my PS5. Many live chats, evidence and months later, I spoke to Playstation Support. They recommended to restore licenses. I did that and went into the addons section, clicked on season pass. There are two options here on a dropdown list that says addons, one "addons" was already installed, and so I installed the other. (Note: There was no drop down before prior to restoring licences.) I then checked Ultimate pack on PS store, it was still unavailable. Finally I went to the game and checked "Manage Game Content" It was all there, it finally showed up and I proceeded to download the berserker packs included in the ultimate pack. Finally!
Settings > Users and Accounts > Other > Restore LicensesGo to the Game > Addons > Season Pass, click on drop down list > Install Season PassGo to the Game > Click options > Manage Game Content
I hope this works for those who still have this issue.
If it does not work, I recommend contacting PlayStation Support just in case, It may be that after I contacted them they fixed the issue themselves on my account and I just simply needed to restore licenses to put the change in effect.
This is what worked for me after so many chats with Ubisoft Support. Still, I want to thank the support team for all their help leading up to this moment. I've notified them of this issue and this fix.