How I fixed lower back pain from over-arching the back during squats

Here’s a summary how I went from incessant back pain -  only doing front squats because back squats were killing me – to pain free stable back squats
It’s a long boring and tortuous story – most of it in my training log here. First step was to join an online lifting community to pick up new cues and tips and then try applying various. I’ve made many a mistake along the way.
The content here is primarily to help those who are over-extending their back at some point during the squat motion

Firstly hip-mobility. The most magical mobility video you’ll find this: Instant relief and effect, and gets better the more you do it. It counts as a magic bullet.

The real tough technique is the stuff about bracing your spine and core. There’s a lot of stuff you can read and watch but it takes a while before it clicks in practicality.
First you need to know where neutral actually is. So, also by Kelly Starrett, you’ll here tips around “external rotation” and screwing your feet into the ground. This was the best explanation for me for the first half (tight glutes)

That move gets your spine into the right position. Now “all” you have to do is maintain that by flexing your abs and holding it all tight. Best general explanation is from this article:
I learned to brace myself into neutral but it took me ages to figure out how to stay neutral as I went down in the squat (since you have to release your glutes from part 1, but keep your abs flex and your ribs in the right place). This hip hinge exercise helped me with the proprioception.

After 2 months of absorbing all the above, I’m now in a world where I know what my back angle is doing and I can keep it relatively stable. All my back soreness is gone…