This is my point of asking. I know for sure that I am no expert on this whole topic, but I do have some excellent results. You are correct in that the 12.5.5 is not as flexible as earlier versions. But I have to say, that from my perspective at least, that 12.5.5 is a sweet spot because with the right attitude and patience, 12.5.5 allows for the installation of 3.1.1. DJI Go 3.1.1 runs incredibly well on my Ipad Mini 2. This is why I still think it is a sweet spot choice. And for that reason only. If someone can get their hands on a mini 2 with 12.5.5, then they are golden. If a person can find an Ipad with earlier IOS versions, even better. Charles Proxy made me scratch my head for sure, but it just required patience and a bit of luck. I agree that you are correct in that the earlier versions are better IF you require legacy installations of products that I am not aware of and do not use.
Here is what I do know:
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12.5.5 Installed on Mini 2
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3.1.1 and 1.8.1 Installed and ROCK Solid performance. I did not bother with 1.6 for the remote, because I never felt a need. Sitting here thinking though, the stick latency is up to 250ms sometimes and maybe 1.6 would solve that.
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32 Channel Installed and ROCK Solid performance.
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1230m from me and perfect signal. I love that in overcast conditions, it is so easy to see the drone.
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This is where I was before starting to work on FW and app versions. I could not go 300 meters without a green screen.
OP, apologies if this post is off topic for your original question about the X3 camera, but people will read these posts and make decisions based on them in the same way that like you, I also made decisions based on Donnie's work. I am not even sure if we are disagreeing about the 12.5.5, but I think it is fair to encourage people that there is good results available with the 12.5.5. That is why I had said earlier that I think it would be good to make these available within the community.
Maybe this is worth having if you go down the Charles route.
Files I highlighted the 3.1.1 number in green, (same as Donnie gave you) on the Go3 page of the excel file. There is a copy of 1.6 for your remote. It sounds like you are squared away with FW 1.8.X. I will leave a 3.1.1.ipa in there for a week. Chances are it will not work because it was downloaded with my apple ID. I had downloaded it with my personal use Apple ID and installed it on the mini. Since then, I signed out of my personal use Apple ID and signed into my business use Apple ID. The DJI Go works fine, so who knows, maybe it is worth a try installing on yours. PLEASE let us know if it works.