I'm also wondering which is better
Do they both have the same vrm or? pairing it with ryzen 5 3600
And i heard B550M PRO4 has some issues with the USB Controller, it keeps connecting and disconnecting even if you are not plugging anything in the back, you just hear a notification sound on your windows, people been complaining about it, even a BIOS update and getting a replacement couldn't solve it.
Its all about how lucky you get, some didn't have any issues at all.