You Could Say I'm a Fan Achievement in Forza Horizon 5
You Could Say I'm a Fan30
Earn a Manufacturer Bonus for a collection of 25 or more cars
How to unlock You Could Say I'm a FanHere's where things get a little trickier. There are - at time of publishing - 5 manufacturers with 25 cars or more: BMW, Chevrolet, Ferrari, Ford and Porsche, but not all of those cars can be straight up purchased. In all of them you need a little Wheelspin luck, to have completed some Accolade objectives and unlocked them in events and what not. So, what does that mean? Well, you should, for starters, ignore Ford, as they have an staggering 58 cars in the game, and in order to get the Manufacturer Bonus, you need to unlock most of the cars (not all). Also, sack Porsche off too - far too expensive across the board, same with Ferrari. That leaves you with Chevrolet and BMW.
So, basically what you need to do is play the game to death and see where you are when you reach the Hall of Fame. If you got lucky with Wheelspins for BMW over Chevrolet, then work on purchasing or waiting to Wheelspin the ones you're missing, but regardless of what happens, you might have to just pray on getting lucky. If you are one or two short though, go to the Car Collection, make a note of it, and then go to search for it on the Auction House. If it's not there, keep Wheelspinning and also looking out for it as a Season Event reward (or even buying it in the Forzathon Shop - AKA the seasonal event shop where you can spend your daily/weekly/seasonal objective currency.