When you had the issue with the GPU was that just in general or were you using it do something specific? Did you update or anything before the issue happened?

Also about your webcam: sometimes they are very light-dependent and unable to achieve steady frame rates particularly if they have auto-focus in a low-light environment.
And in OBS itself your webcams all have varying settings that you can adjust.
The codec can be very important. It's a drop-down list on mine and it has a few options that are nebulous like y4l, y4m-emulated, and the slowest one is mpeg I think.
I would def see which one of those it prefers, and also set the frames per second & the resolution to the one the webcam advertises.
At the very least lowering the FPS/resolution should often result in smoother performance, and making sure it has enough light.
There's a lot of variability in webcams, and OBS tries to make sure any of them can work.
Droidcam has no fuss whatsoever because your phone is doing all the work on it's own and sending the video to OBS.

The integrated webcams on new laptops with Linux can be a real pain I THINK because the laptop's firmware is trying to use it as a light sensor to adjust screen brightness automatically.

IF you are using OBS I would definitely make sure you have the video-encoder in the main settings set to NVENC capture because your GPU can just feed it the frames as it renders them. But yeah multiple cameras including Droid-Cam should be no problem on a newer computer especially with NVENC.