I can't seem to find any specs on your motherboard from Gigabyte or anywhere else. Are you sure you have the right model listed.
However under the circumstances if it is a B550, regardless of the manufacture, I have not found any that support PCIe 4. They support PCIe3.
The X570 boards will support PCIe 4, that is unless you are running a 2nd Gen CPU (2000 series). Even though the board supports PCIe 4 it will drop back to PCIe 3 speeds.
Now that I have said that, your Radeon 6000 series GPU is a PCIe 4 GPU running in a PCIe 3 slot.
PCIe 3 x16 has a 16 GB/s transfer rate whereas the PCIe 4 x16 has a 32 GB/s transfer rate. This means that your GPU is only going to be able to access 1/2 of the bandwidth it is capable of. There are websites that will tell you differently but the math doesn't lie. I have experienced this with an XPG GAMIX S70 PCIe 4 NVMe 2.2280 SSD first hand. It's maximum speeds are only 1/2 of what they should be because the machine I have it in has a Ryzen 7 2700 CPU (does not support PCIe 4). So the PCIe 4 SSD drops back to the PCIe3 transfer rate.
I hope this is clear enough to understand and it may not address part of your problem. It has to do with compatibility to get the best performance of the product you are using.
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