I received a reply from FORZA support asking me to turn off the design of Drivatar, so I tried it, and the symptoms of continuous stuttering right after the start of the race and a drastic decrease in FPS in the second race disappeared.
Other settings are as follows:
The stutter and VRAM overflow seem to be caused by car painting.
(In testing, we saw that every time a stutter occurred, the design stuck to the Drivatar car.)
We’ve managed to get to the point where we can play the game, but how long will we be allowed to verify the operation of this game …?