The B650M is a smaller size and therefore has less features, but overall they seem similar. Biggest difference would be the integrated SSD heatsink and better VRM design + cooling of the non-M version. Also the second SSD slot being connected to the CPU instead of the chipset, if you ever want to put in two M.2 drives. One thing to watch out for is that both of these boards use a Realtek LAN chip which sometimes can be problematic with Linux.
Parannoul - Beautiful World. If you like it, check out his albums, especially To See the Next Part of the Dream and After the Magic