Webcam placement in OBS is the fifth stop. The webcam source needs to be added to your Live and Just Chatting scenes, sized appropriately, and positioned in a corner of the frame where it will not crowd other content.

The configuration in the Live scene: click the plus icon under Sources, select Video Capture Device, name it (something like "Webcam"), select your webcam device from the dropdown, and click OK. The webcam appears in the OBS preview. Drag it to the bottom-right or bottom-left corner. Resize it to roughly one-quarter of the vertical frame height.

The Just Chatting scene gets a larger webcam, sized to roughly half or full vertical frame height, positioned with breathing room around it.

The discipline: lock the webcam position once you have set it correctly. OBS lets you lock individual sources to prevent accidental drag during stream. Lock the webcam in each scene. Resist the urge to "improve" the position mid-stream. Consistency wins.