Not sure if this helps, but e-sims are extremely cheap and can be set up on the go through an app these days. You could get a 5g plan in the area with bad internet and use it as a hotspot to download content to your other devices. I use Nomad, but there are a lot of providers with plans that are unlimited or pay by the gig—all affordable with time periods as short as 7 days.
A $10 solution, in a pinch, is a good choice.
I got an email saying I would get iOS Test Flight instructions soon.