I managed to sort it out thanks to this guide:
https://forums.gta5-mods.com/topic/14693/quick-start-guide-to-modding-grand-theft-auto-v(https://forums.gta5-mods.com/topic/14693/quick-start-guide-to-modding-grand-theft-auto-v)

Closing thread

@JohnFromGWN
Sadly none of this worked. I used to mod my game a lot about a year ago, and I stopped and kept the base vanilla game (except for the trainer) but now they all seem to be rejecting any additional DLC I add to the mod update.rpf file.

So I am not sure what the issue is, because I have another mod: Fort Zancudo Off-Shore Military Base [YMAP/MLO] installed and working fine. But whenever I try other mods like these:
Ford Mustang GT NFS + GT500 2013 [Add-On] OR 2019 McLaren Senna [Add-On], it constantly crashes when loading the game. It seems like its only for car mods because I have tried almost 5 different ones and the result is the same. But the fort zancudo one is a map mod and that is working fine.