I've recently added an Arc A310 to my B450 motherboard in the 2nd PCIE slot (used for AV1 encoding only). However my B450-TUF limits the 2nd slot to PCIE 2.0 and it is creating issues (no issues in top slot).
Hoping there is some people who have recently upgraded to Ryzen 7000 looking to get rid of their old mobos.
Most dual slot B550 should work and all X570 are supported
Based in Christchurch if this helps :)
P.S - also happy to send the B450 in a trade if you are still wanting a spare motherboard.