Went to your Gigabyte Support Motherboard QVL List for M.2 devices (10/07/2020) and it does show as being compatible: https://download.gigabyte.com/FileList/Document/mb_m.2_support_amd_201006.pdf
But when I look at the SSD QVL LIST (08/24/2020) for your motherboard it doesn't mention the 980 Pro: https://download.gigabyte.com/FileList/SSD/mb_ssd_support_amd_200819.pdf
The M.2 List is newer than the SSD List so it looks like your Samsung 980 Pro is compatible.
EDIT: Here are the Specs for your Motherboard concerning the M.2 slots and processors that support it: https://www.gigabyte.com/Motherboard/B550M-AORUS-PRO-P-rev-10/sp#sp
Seems like the only M.2 socket that support PCIe 4.0 with a 3rd Generation Processor is M2A Socket.
M2B supports PCIe 3.0 because it uses the CHIPSET instead of the CPU.