Connect webcam to mac mini m4

most adaptors from usb-a to usb-c should work fine, it's just a connector shape adaptor with not electronics or the likes, as long as the adaptor is a cheap one which only connects the power pins for charging them it should be transparent for the mac that the connected device did not came with an usb-c connector in the first place,

when it comes to webcams then I usually go for logitech myself

Like Rudegar, I always recommend Logitech. I have Logitech "HD Pro Webcam C920" attached to my M4 Mac Mini and it works great.

Also, do not forget that the monitor that you have connected to your Mini may have a USB hub that has USB Type-A ports available. These ports on the underside of my monitor are what I use for my webcam. To connect the monitor's USB hub to the Mac Mini I purchased a USB 3.0 Type-B to USB Type-C adapter cable from StarTech.

Rudegar wrote:

as long as the adaptor is a cheap one which only connects the power pins for charging them it should be transparent for the mac that the connected device did not came with an usb-c connector in the first place,

Did you mean to say that "as long as the adapter is not a cheap one which only connects the power pins …"?