Matx B450 board
Matx B450 board
I searched for a MATX motherboard near 110 USD and found the ASRock B450M Pro4 with AMD AM4 socket. It should fit your Ryzen 5 3600 and RX 5700.
Here’s a neat collection of motherboards ranging from Itx to Atx. You can evaluate the various options. The more advanced the tier, the better the performance usually is.
I recently purchased two Pro4 units, both of which received updates—one from Newegg and another from Amazon. A friend also bought a steel version from US Amazon, which was updated as well. It seems we're moving away from this model phase, especially around the middle of its life cycle.