The audio is only producing on one side because the camera is recording the external microphone as a mono signal while the clip is expecting a stereo signal. Typically the easiest solution to this is to duplicate the audio to both left and right tracks when you are editing your clips in your preferred video editing software.
Is it supposed to take a TRS 3.5mm mini-jack? I saw a YT video where it says that it should because it's a straight in signal for a microphone. The TRRS is for smartpones or laptops that use the same port for microphone and headphones. Trouble is, it that I can't seem to insert the TRS into the port, and it only goes in so far. I'm afraid if I put pressure on it I might damage the port.
I replying to my own post because I finally found my answer. Canon does not specify much in their Vixia HF R800 manual about the audio port, and for that reason we are left to search and search until we find answers. I recommend they be more detailed about their products. I love this camera because it is easy to use for the price and has great quality. That being said I only have an issue so far with the audio.
As it turns out, it does not (or should not) take a TRRS minijack because those are meant for devices such as laptops and cell phones where the same port is used for both in and out going signals. What is needed is a TRS mini jack, and now to my fearful dilemma. I was afraid to give that TRS minijack the extra push into the port for fear of damaging the port. But this morning I gave up in frustration and pushed it in until it finally snapped into place. I was glad! Now I can use a proper minijack meant for the camera. So my advice is this; If it doesn't seem to fit you may have to push it really hard to get it to go in. You can decide for yourself in case you were having this problem as well. And my thanks to Mark35mmF2 for his response.