The update runs perfectly with 2x 32 GB @3200 Mhz (1.2V) @1.35V and a 4750G with BIOS 3.60R Beta. A second system with 2400G and 2x16 GB @2400Mhz also runs stable. Like the previous speakers, I would therefore point to the RAM itself.
Good luck

I reset the BIOS to factory settings via CMOS reset after the BIOS update 3.70. As I said, both sticks run without problems as long as they are used individually. It does not matter whether stick A or B and slot 1 or 2. All combinations work as long as only 1 stick is used. Memtest has already been carried out. The CPU is not overclocked. I have now bought a 16GB stick and it has been running without problems for 12 hours. A Ryzen 3 3200g with standard clock speed is installed.
Many thanks for the helpful answers!
If I do need dual channel, I will downgrade the BIOS to 3.60.

Switch off overclocking of the RAM bars if activated. WIN 20H2 runs without problems with Bios P3-60.
Would swap the RAM. Use this with a 3400G: HyperX Impact HX429S17IB2K2 / 2933MHz DDR4 CL17 SODIMM

Runs here with CPU 3400G and 2 times 8 GB SO-DIMM without problems with the latest versions. SSD is an NVME 1 TB Intel 660. Perhaps it is also due to the RAM? Or is a 4000 CPU installed?