Is there any way to record external audio from a Canon Rebel R6?
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Bad news first- 

Unfortunately, you are stuck with the in-camera mic with the T6. The T6i has a microphone jack for mounting an external microphone. If you want to mount an external mic to a Canon Rebel T6 body and record that audio stream to the same SD card, that's really your only option. 

However

Can you elaborate a little on what your uses for the video are and what your workflow is? 

I have shot on a T6 and T6i extensively and I eventually determined the workflow that was best for me was to use a Zoom H4N as my primary sound recorder (placed somewhere out of sight in the shot) and synced the audio streams together in Adobe Premiere during post production.