Google changed the description with the November-Update today and it seems that they've mixed it up previously.
So the current regional versions are:
RD1A.200810.020, Oct 2020, AU & JP carriers
RD1A.200810.020.A1, Oct 2020, KDDI only
RD1A.200810.021.A1, Oct 2020, EU carriers
RD1A.200810.021.B3, Oct 2020, Verizon
RD1A.200810.022.A4, Oct 2020 (global?)
RD1A.201105.003, Nov 2020, JP carriers
RD1A.201105.003.A1, Nov 2020, AU carriers
RD1A.201105.003.B1, Nov 2020, EU carriers
RD1A.201105.003.C1, Nov 2020 (global?)
Anyway. As said, I bought my Pixel 5 from the german google store and not from a german carriers store. So I expect to be on "RD1A.201105.003.C1" instead my phone updated to "RD1A.201105.003.B1".
Still confusing but at least the "KDDI only" - discussion is solved. I guess. ?
Isn't the C1 version for the US carriers? That's probably the firmware/image file that has support for the mmWave hardware in the US models.