Rocksmith 2014 from PS5 store is the digital version for PS4. There is no PS5 version of Rocksmith. So its the same on PS4 and PS5. Same for DLC. All bought PS3 DLC is transfered to PS4 for free. And PS4 DLC is what you see in the PS5 store.

Afaik all DLC from PS3 is also available in PS4/PS5 store, because of this free transfer thing. Only thing that could be a little complicated is the import of Rocksmith 1 songs to RS14, if you haven't done it yet. So, I would do it asap before the PS3 store will be shut down. If you need help with the song import, feel free to ask me here. Its quite tricky, if you don't know how...