Not to sound paranoid, but won't even LinageOS phones have to run closed-sourced firmware and drivers?
I don't think you can trust any proprietary firmware out there, its just a question of which you trust less than the others.
Simple. I do not "trust less". I just do not trust. My phone is a phone. No Internet activity. I spend enough time in front of my desktop, dragging another computer anywhere I go is the last thing on my mind.