The failure definition topic is always an interesting one. I think we’ve had it here a few times.
For me, muscular failure is the inability to complete another concentric (and I’m including getting sloppy as an option).
So, for compound movements, I am not going to go near that. I definitely used to when I was younger, to the question above, and that indeed meant the squat bar was going to be on the rack pins and I’d have to crawl out. I stay so far from that it’s fair to say I’ve redefined failure to be “technique breakdown”, as also noted above.
On smaller moves, I’m not afraid of failure; can I really ruin tomorrow with a barbell curl today? I still think there’s a difference with failure between low reps vs. high. Like if I get 2 reps and can’t get a third, I may still have some juice left, just not enough for that weight. The lighter the weight gets, the less muscle it takes per rep, the closer I think I’m getting to real muscular failure. Get to true concentric failure on a set of 3 dumbbell curls and then on a set of 25 and there is a difference!