“The touchpad ribbon is connected to the motherboard by a connector that flips to tighten and loosen” —> Just fixed a controller I bought in 2017. There was definitely no flip connector there, the ribbon simply went in. I guesss the internals changed. So beware: don’t mess with the female connector on the motherboard if there’s no obvious flip switch.

In the second picture I was originally wondering what that diagonal piece of material was. Now that I've done a repair I can say that it's the sticky adhesive around the edge of the phone lifting up with the screen.

Yeah, I kept applying more heat only to realize the same thing. The gold contacts are sitting on a very thin flexible plastic strip that you need to peel up.

Also skipped this step.

Yep, brilliant piece of advice. I would have missed the white diffusing paper if not for this comment. Thanks!

Wow, thanks for this comment, this saved my hide. I suspected that I was a bit offset after reattaching the shield and sure enough it was slightly hitting the vibrator. It took a while but I was able to get the shield all the way to the left by hooking the little metal clip on the left side of the shield under some plastic that its supposed to go under. (Recall that when you take off the shield you have to slide it out a bit to the right.) This shield and all the stuff under it is very difficult to get right when closing up the phone.