Yes the Motherboard has one PCIex16 2.0/3.0 slot. But your GPU card will run at PCIe 3.0 x 8 speeds.
According to TechPowerUp, https://www.techpowerup.com/gpu-specs/radeon-rx-6400.c3813, the GPU card is compatible with:
Bus Interface
- PCIe 4.0 x4
PCIe 4.0 x 4 is the same as PCIe 3.0 x 8 and PCIe 2.0 x 16 slots
