Hello, I bought the premium pack a couple of years ago and now there are many cars and tracks on the game that i don't have. How could i buy every content that i don't have easily? (without adding every car one by one on the cart)
The easiest way is to create a new steam account and buy the premium pack again for the new account. The cheapest way could be to by individual packs like GTR3 or DTM21 as suggested by @FeltHλt and also to use VRP and or wait for the next sale - Halloween, Black Friday, Xmas but there is no guarantee there will be a sale then.