Do you remember which firmware you have? I just recently upgraded mine to V1.35, and still have the .zip file from Unication. You could email them and ask for a download link, or I can send it to you if you wish.
Honestly, I don't have a clue why you're having so much trouble. I've had my G5 since 2017, and it's been used & abused ever since. I've done several firmware updates over the years, and I've programmed it several hundred times without fail.