JPEG is a lossy compression format, which means that it throws away some data to achieve a smaller filesize. Most of the time, this doesn't really matter because the algorithm is very good at figuring out data you don't actually need when it throws it away, so it's usually impossible to see the difference between a raw image and a JPEG copy at reasonable quality, except that the JPEG will be about a tenth of the file size.
The problem comes when you edit an already-jpeg-compressed image and save it again.
Basically, any time you re-save a JPEG (i.e., save it, close it, open it again, save it again), it loses even *more* quality, and that quickly becomes noticeable. If you do it multiple times, the quality gets exponentially worse, and the output from your Rebel T7 ends up looking like a particularly cheap cellphone.
E.g., I bought an original Canon Digital Rebel a few months back on a whim, and even though your camera has four times the pixels and even though I was shooting at (for this camera) high ISO, my shot has more detail just because I started with a RAW and had an editing workflow that didn't save it as jpeg multiple times.
(Don't come at me for this photo; it's not very good and was just a quick "Hey, I got a new camera to play with, can I take a picture of you in shitty lighting with it while I'm on my way out the door" shot. It's just meant as a demonstration of image quality)