very simple. best solution right here. not sure why the others are so complicated, yet also leave out key info.
from the Go Race tab, choose Rivals, then choose Time Attack for whatever Class you like. go right to the Daytona Tri-Oval or Indianapolis Oval and press Y to show the leaderboards, then press X until you see Friends scores. pick one that has a flagged lap (triangle with ! inside). if you don't have any flagged laps, go back and choose Tri-Oval at night, or try another Class. Indy is shorter, but Daytona has softer curves which you may prefer since you won't be using the line.
now choose your car. if you absolutely cannot drive Manual, you can buy the Tesla car, which has only one gear so no shifting is required. however, all you need to do is go around the track once without messing up so Manual shouldn't be a big issue. at the pre-race screen go to Assists. you need the settings to be Off, ABS Off, Normal OR Simulation, Off, Manual w/Clutch, Simulation, Off.
all you need to do is complete the race with no collisions. if your time is not flagged then you will always beat the flagged time. if you mess up, just go around another lap until it says you beat your rival. now pause and choose Finish Race. go back to the leaderboard and select another rival with a flagged time, even the same one works. repeat until you reach 10.