yeah 3rd what everyone else says, your form isn’t near as bad as I was fearing.
Look at your all-time max video, then compare it with the first 2 videos and the vid of 405 x 4. Noticing the differences between your best pull and your subpar pulls will help you find what needs to happen. I’ll give you a hint: your 405x4 video is a lot closer to the form you used to pull your max than the others and also looks the best.
You’re tight, you keep it together well. The biggest issue that jumps out right way at me is your head. Look where your head is tilted in the max video, then look where it is in the first 2 videos. You’re looking STRAIGHT DOWN in those. In the max video the head is up a bit more and looking slightly out. Never look straight down. That doesn’t mean stare at the ceiling, but don’t stare in front of your feet.
Start and pick a spot about 10 feet in front of you to look at when you start pulling. Stick with this spot for about 4-6 weeks to give yourself some time to get used to it, then if you don’t like it adjust the spot a little. Spots tend to change over the course of years as pull styles and strengths change, so it is ok to revisit it and tweak it. You just shouldn’t change it every set or every week. You won’t ever find your comfort zone if you don’t get some time to acclimate to a new spot visually.
Second thing: your lock out seems to be mostly back. You need to get your glutes involved more. Don’t think about leaning back to finish the pull, think about squeezing your butt as hard and quickly as possible after the bar gets to about your kneecap.
In terms of training I’d suggest more pull-throughs at heavy weights to really hammer the glutes, focus on the same thing: squeezing the butt as hard as possible to finish every rep. I’d also recommend some paused leg pressing using your deadlift stance (make sure your feet go high up on the foot plate). Pause in the hole 3 seconds on every rep, then drive. Do that for higher reps (6-10).
A good coach always helps, but I think those will help you. Do you fail in the bottom of the pull, or about mid shin, or where?