The latest generations of gnss receivers have spoofing and jamming mitigation and detection features included with the chip, and multi-band rx technology to sync to more constellations simultaneously and do exactly what you’re talking about. Before then, the spoofing/jamming detection would likely need a software implementation after the receiver. There are different types of spoofing/jamming, all of which are detected and mitigated in different ways.

I don’t know the commercial aircraft industry standards for updating technology, but I wouldn’t be surprised if most commercial aircraft don’t have what you’re talking about.

It means for the first 20 years they spent all of their profit on expansion / R&D

Yes, you can code in machine code. I did it as part of my CS Degree. In our textbook was the manual for the particular ARM processor we coded for, that had every processor-specific command. We did that for a few of the early projects in the course, then moved onto Assembly, then C.