I had a Canon T8i (body only) on order since March 2020 and finally received the camera in September. My current camera is a Canon SL1 (purchased in 2013), so the T8i should have been a nice upgrade since it has a lot of great features. I really wanted to like this camera. However, after using the camera for a couple of weeks, I returned it.
The photos taken with the T8i were not very sharp (even with back button focus, which I usually shoot). I tried the camera under different conditions (landscape, portrait and just general shots). The quality, in terms of how the photos look (exposure, color, saturation, etc) were great, but many of the shots were "soft" (slightly out of focus). For portraits, the T8i would nail focus about 70% the time. It seems that if I shoot in "Live View" that the focus was accurate. However, "Live view" is not something I care to use all the time. I mainly shoot single focus point using back button focus and I struggled to always get sharp photos. I tested a variety of my lenses (Canon and 3rd party) and saw similar results. My trusty SL1 had perfect focus under the same side-by-side conditions.
Another thing that was strange is when shooting outdoors in sunlight using Program mode and auto ISO. Often, the ISO would jump to a range of 2000 - 3200. I have never ever experienced this with my Canon SL1 or any other DSLR I have used in the past. Because of this, I set the camera ISO restriction to an ISO maximum of 400.
Another thing that annoyed me was the optical viewfinder. It was smaller and darker compared to my SL1. I shoot almost 100% using the viewfinder versus the LCD Screen so this was disappointing.
Note that my test photos were JPG format and the camera was set to the highest resolution/image quality setting. All photos were shot using either Program mode or Manual. There were not any firmware updates available.
As a side note (not an issue with the camera), I needed to send one of my Tamron lenses in to get a firmware update. I was getting occasional purple and green fringing which was pretty severe. The lens firmware update should have fixed this, but I was not able to confirm since I returned the camera before the lens was shipped back. Turning off all in-camera lens corrections helped minimize this issue, but it would still sometimes happen.
So, that is my experience with this camera. Some of what I mentioned might be OK for some, but I definitely felt that it was a step backwards from my Canon SL1.