I have 2 identical 4Bs: the one older one that used to work and the new one I ordered yesterday.
With all the same cables and SD card, the new one works fine, the other one is giving me the rainbow screen.
Does this mean the other one is irreparably broken? I ask because it seams really weird for a computer to be perfectly able to produce a rainbow pattern but then not being able to boot any further than that. Hardware failure usually results in total failure.
So is there a way to revive the old Pi? I tried both NOOBS and Buster but both only work on the new one. I also used a 3Amp USB C supply and didn't get any lighting bolts on the new one.