To stop audio clipping in OBS, add a Limiter audio filter. 

This acts as a digital brick wall to prevent your microphone or desktop audio from exceeding 0 dB (the point where distortion occurs).

Follow these steps to set it up:In OBS, locate the audio source in your Audio Mixer and click the three dots (or right-click the gear icon) next to it.Select Filters.Click the + (plus) icon in the bottom-left corner of the filters window.

Choose Limiter from the menu.

Set the Threshold to -3 dB (a safe standard to ensure nothing distorts).
Set the Release to 60 ms.

If your audio is still clipping before it hits the limiter, you may need to reduce your physical hardware gain (on your audio interface) or lower the fader in your OBS Audio Mixer until your peaks stay below 0 dB.