In addition to being an assembly language programmer, I am also an electronics engineer/technician (with probably "similar level of experience", or even more), and therefore, with knowledge of both areas, I can think of hundreds of different ways of being able to build something that generates random numbers, and of high quality (for example, based on white noise generators, which are the thermal noise of semiconductors, try to predict this with supercomputers). Therefore, I don't think this is by far the most difficult part to do on an x86-64 processor, for the Engineering elite, present in the Intel and AMD teams, for example.

Furthermore, I must say that I have not yet received any further feedback from AMD regarding the case. But they have already escalated my case internally with them, so I am still here waiting for a precise update from them, to share it here. And, since 9 days before posting here, until the present moment, not a single 0 came out of the 2 AMDs that I had access to!

With the new update I made to my application to test this, it is now also possible to benchmark the random number generator, and it is also now possible to run the test on processors that do not have the 'rdseed' instruction. As for the benchmark, it is surprising how different the results are between different processors (e.g.: a Core i5 from 2012 generates 12.6 M numbers per second, while a Core i7 7700 from 2017 generates "only" 750 k numbers per second, and my AMD Ryzen 7 around 2.6 M numbers per second, and the AMD generator being completely inert to clock variation, and the Core i5 from 2012 100% dependent on the clock, as it seemed to me in the tests I did). Which leads me to realize that the random number generator circuit must have large differences, and probably completely different versions/revisions, even for models from the same manufacturer.

So far, I also have not found decent information on how their RNG unit works.