I'm very confident this just isn't possible. If you want something with 4G/5G, you just cannot get open hardware. Without open hardware this is a moot point. There are a number of projects where you can use RISC-V hardware with 2G and even 3G open source hardware, but calling them equivalent in any way to an Android or iPhone is a... stretch.

I think the issue is the patents with the hardware needs to run out, but by then 6G or 7G will be out and you'll have the same problem. Anything with DMA that isn't closed source cannot be trusted. I'll die on that hill.

Even with projects like PinePhone, the best they can do is a privacy switch that turns off the modem. It's just not good enough to take it seriously.