Don't you mean the Sports/Racing game of the year?
A few people have noticed the same thing. Someone on reddit came up with a fix. I haven't run into the same issue so I can't verify it'll fix things but others have indicated it helped. If you have at least 16GB of ram it can't hurt to try.
"This is the real problem why the game has all this bugs in game like fps drops or shutters its because of memory overflow something is wrong there the game is taking not enough RAM to reproduce the graphic like its not possible that players with an RTX3070 and an good CPU getting shutters in game. This is how to fix the problem, that the game is using your full RAM like 16gb needed to play on high or ultra settings: Memory overflow is another cause of the LOW FPS issues after playing Forza Horizon 5 for a while.
This can be fixed by increasing the paging file. Type “advanced system settings” and open this app > click “settings” under Performance > Advanced tab > click ‘Change’ under Virtual Memory > uncheck “Automatically manage paging file size” > check Custom size and set 8192MB for Initial Size and 16000MB for Maximum and hit apply. The paging file size I’ve mentioned here are for at least 16 GB of RAM. This will fix the low FPS issue with FH5."
The seasonal events this run are actually tough. They are very dependent on cornering and setting up well for the next corner.
Basically stay very wide approaching corners and ignore the racing line even to the point it seems stupid. You'll end up with less braking zones, keep your speed up and not slide sideways around the corner which is where you'll lose even more speed. You also need to be in something relatively light so your inertia doesn't drag you off your line.
Crudely draw example of a typical trailblazer corner. Yellow dots are checkpoints. The light blue line is how the game's racing line generally lays down. It's a very conservative line made for beginner racers that really becomes mostly useless at higher levels or against human players and following it in trailblazer races put you at a disadvantage. Following it will keep speed lower than if you make some adjustments to it. The red line is what I would use. This way I brake hard once, then start my turn, feather the throttle until I'm generally facing the right way and then mash the gas. I'll be straightened out while the other racers are still working their way around the corner accelerating the entire time.
The big jumps are brutal too, you absolutely need rally springs and a lot of travel damping to soak up the landings without scrubbing speed.
I built a Bronco with off-road tires and a tune specifically for Pick Up the Pace reducing it's weight. The big trucks need to scrub too much speed and the small ones lose too much speed when hitting things like walls. Medium weight vehicles are a good middle ground and I get to stick to my "only mods that make some sense" rule I self-imposed. For Four on the Floor I used a JCW Mini Countryman set up with off-road tires and a tune and for When it Rains it Pours I used the newest Audi TT with off-road tires set up similarly.