What GPUs are compatible with a Ryzen 5 5600GT and A520M K V2 motherboard?

Almost any GPU made in the last 20 years will fit with your setup. Just be mindful of your power supply. If it’s underpowered, it could cause issues. What wattage do you have?

You'll want to look for a GPU that supports 16 lanes of PCIe 3.0 or newer. Good news is, any GPU from the last 15 years should work just fine! They are backward compatible, so if you choose a newer model like PCIe 4.0 or 5.0, it will still work, though you might not unlock its full potential with your current motherboard.