Instead of getting 1, 2, or 3 free throws, you would get 1 free throw worth 1, 2, or 3 points, respectively.
The only changes I can see, in addition to reducing the game time slightly, would be making it harder to get substitutions in after a foul and some extra pressure in close games where the team that's behind is fouling. I think it could be worth a try.
https://basketball.realgm.com/wiretap/235059/NBA-Considered-Eliminating-Multiple-Free-Throw-Attempts
The only changes I can see, in addition to reducing the game time slightly, would be making it harder to get substitutions in after a foul and some extra pressure in close games where the team that's behind is fouling. I think it could be worth a try.
https://basketball.realgm.com/wiretap/235059/NBA-Considered-Eliminating-Multiple-Free-Throw-Attempts