Make sure you have the monitor(s) connected to the graphics card, not the motherboard.
Check in Adrenalin software which GPU is labeled as #1 and which is #2.
You could also disable the integrated Radeon Graphics, either in Windows Device Manager or in the system BIOS.
Ryzen R7 5700X | B550 Gaming X | 2x16GB G.Skill 3600 | Radeon RX 7900XT
Ryzen R7 5700G | B550 Gaming X | 2x8GB G.Skill 4000 | Radeon Vega 8 IGP
Ryzen R5 5600 | B550 Gaming Edge | 4x8GB G.Skill 3600 | Radeon RX 6800XT