My goodness Tom… YOU ARE THE MAN!!! I bought a used UAP-LR off ebay to provide wifi in my garage. I didn’t care what went out there… I just wanted to be cheap. Unfortunately, I got it stuck in an upgrade loop. It had 2.x firmware on it and here I was trying to get it to upgrade to 4.x. Well… Armed with this video (and a little googling) I was able to get it upgraded.
I will add… my only difficulty was I had to add a couple extra arguments to get ssh/scp to work. Things got deprecated since this AP’s last update. I had to add -c aes128-cbc -oKexAlgorithms=+diffie-hellman-group1-sha1 to both commands to make things talk.