That’s bullshit.
you can train all day if you want to as long as you take enough time to recover during sets
I knew a guy who used to be a powerlifter, used to take 3 hours on a squat session, probably did 20 sets tops in those three hours rep ranges from 20 down to singles
Spent more time talking to people than he did train, did it work for him yes, did he have big ripped legs , no of course not.
Look at Fred Hatfields legs compared to Tom Platz, they both trained legs with heavy squats.
You can get as much stimulus out of 3 good sets and you can out of thirty.
Take a muscle to total failure, put the bar down and wait 30 seconds and you can go again for a few reps, is it doing you any more good than stopping on the forst set, probably not.