@solokwa regarding 4-6 sets, no for 90%+ of lifters. honestly, i think more people would be better off admitting they don't know how to push to failure and accepting that, doing more volume, practicing the movements and training this skill for years until they actually can push themselves to that level. everyone and their mother says they train to failure but i just don't buy it. i'm not above it either - i trained my whole first year to "failure" low volume and did well strength numbers wise but as soon as i added more volume i actually grew. looking back now - i can tell you i was not going to failure even though i would swear up and down i was - and im sure in a few years i'll look back at how i train now and laugh at some sets i thought were to failure. every session is a chance to practice this skill and it does develop - but imo, if you don't do the additional volume to compensate then you're missing out on gains.
true failure means every rep is with max effort concentric - with max force output - and once you're not able to complete the full concentric. i literally have never seen someone do this in the gym barring powerlifters or 1rm testing. you need to be doing this every single rep and the measure of failure is when reps slow to the point where a 1 second rep is taking 4/5/6/7+. most people i see are just matching their force/effort to whatever load they have on the bar to keep the concentric controlled and i barely see slow down for later reps. take video of yourself if you want to check. easiest way is to do warm ups using max effort concentric full force - the weight should be flying. then once you get to using your working set 10RM or so - the first couple reps should be flying at the same speed as the warmups - if they're not, you're not using max effort and you can't say you're training to true failure. then, the last 2/3/4/5 reps should be slowing considerably and your last rep you should fail the concentric - but you should be outputting the same force for each rep. if you're not doing any of that - it's not true failure
all that being said, if you're actually doing the above, yeah, 4-6 working sets and probably even less is more than enough. most people aren't, should just accept it, and then adjust their training accordingly by doing more volume. which ironically is why most volume studies show more volume is better, and many people are able to make very good progress without having to train like this. you'll get better and better at pushing to this over time and naturally volume will drop - which is why tons of advanced guys advocate for it.
sorry for rant