I use Droidcam OBS with OBS on Windows/Mac and it's pretty good, especially over USB. Droidcam X is good as well but with OBS you get more control over the image quality and you can do some arranging of the scene as well.

There's also https://vdo.ninja/ (previously obs.ninja) that doesn't require any special apps. You open up a browser on your smartphone and input the link into OBS as a browser source. The performance on Chrome is superior to other Android browsers in my experience. There's a bit of delay and the quality isn't quite as good as OBS as the connection goes through the internet and isn't local, but the delay is actually surprisingly small.

I use camo which works really well but I am mac/ios so don’t know if they support other platforms.