What lens or lenses are you using with the 80D? And at what aperture?
Are you using a particular focusing point when taking photos? e.g. the center focusing point when at f/2.8 allows for conditions to be down to EV -3. However, when at f/5.6, the center point allows for conditions down to EV -1. And when using other focusing points at f/5.6, conditions can only be as low as EV -0.5
For reference, these Exposure Values (EV) are roughly:
Yes! First reset it back to factory defaults. Check your manual if you don't know how. Now on a nice sunny day set the 80D to P mode. One Shot, not Ai-servo, and select just the center focus point. ISO 200 and Daylight WB. Make sure the lens is on AF. Take some random shots outside of various subjects if they are all OK there is nothing wrong with the 80D.
Your dark low light shots are probably beyond the ability of you camera/lens combo as all photo gear has a limit to what it can do. However the simple test above can mean the low light issue was user caused. The same settings that you used for the test can be used for low light. Simply adjust the ISO number to a higher number. ISO 3200 for instance. If the camera still can not achieve focus you may have reached its limit.
The A/F options on the 80D appear to be much more sophisticated than I had imagined. Here's a link to the online user manual if you don't already have it. Start on page 115 to see all the options.
Don't some Speedlights offer the option of providing an I/R beam or focusing grid pattern to assist with low light focus conditions? Though that may still not be helpful for taking night time wildlife photos.
In live view mode, it might focus sometimes in less light. Also in live view it will focus when using a lens that is F/11 or F/13 wide open because in live view the EOS 80D is using dual pixel auto focus similar to the newer mirrorless cameras. I occasionally took advantage of this on my EOS 80D to use a 2x teleconverter with a lens that was F/5.6 wide open.
12/05/2023: New firmware updates are available.
09/26/2023: New firmware updates are available.
08/18/2023: Canon EOS R5 C training series is released.
07/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
03/30/2023: New firmware updates are available.