The complete description as per Motherboard manual is:
AMD B550 Chipset
∙ 4x SATA 6Gb/s ports
∙ 2x M.2 slots (Key M)
▪ M2_1 slot (from AMD processor)
▫ Supports PCIe 4.0/ 3.0 x4 *
▫ Supports SATA 6Gb/s
▫ Supports 2242/ 2260/ 2280 storage devices
▪ M2_2 slot (from AMD B550 chipset)
▫ Supports PCIe 3.0x4
▫ Supports 2242/ 2260/ 2280 storage devices
* The supported specification depends on installed processor.
Regards