1.100.000 was just my experimenting.
the 1.500.000 is right on the page you put a link to:
It says:

Debug: one Debug UART, 4 Pin 2.54mm header, 3V level, 1500000bps

I'm trying to use the debug UART of the Nano Pi M4. I connect via PuTTy. I set correct COM number, speed 1500000, but all I see is garbage. I was expecting the log of the system boot and be able to issue some commands after boot sequence is complete. I installed latest FriendlyDesktop on SD card. I'...