If you have a spare unused SD card, you can do some trials.
First, put the unused card in your camera and format it there. This is to ensure that the camera will be able to read it. The logic behind this is that the camera should be able to correctly read and write any card it's able to format. If it can't format it, then maybe there's a problem with the brand of the card, or its capacity. Some older cameras will balk when given very large cards. Basically, there were no such cards in existence when the camera was made, so they don't know how to deal with the unexpected capacity.
Second, if you have something other than the camera that will read and write cards, you can remove the card from the camera, put it in the other device, and see what happens. As a test, shoot a couple of photos on the newly formatted card, so you have something to look at in the other device.
If you don't have anything else that will read SD cards, then your only option is to try reading and writing to the card while it's in the camera, connected to your computer. Do this on the spare card, not the card that has important images on it. You'll basically need to read the instructions on how to write things from a computer to your camera, or just look it up in the camera manual (or camera software manual) to see if that's possible. It might need specialized software, i.e. something other than Image Capture. The Canon website has manuals for cameras and software.
Once you've written something to the SD card from the computer, unplug the cable and see if you can review the images using just the camera. If it works, you can try more images, or maybe some movies instead of still images. Basically, if you want to review something in the camera, upload it from the computer and see what happens. Since it's all happening on the spare SD card, you can't hurt anything.
It's entirely possible that there's no way to write images to the in-camera SD card using just the computer. It depends on the camera and the software. Find out by looking on the Canon website.
If there isn't any way to write to the camera, then the only option is an SD card reader. I have a Transcend model from years ago that still works great. It's easy to find them on Amazon or other vendors, and they are not expensive.
If you have an SD card reader for the computer, then you should always slide the write-protect tab on the SD card to the NO-WRITE position before putting the card in the card reader. Although not entirely fool-proof, this will prevent things like Spotlight indexing from happening, because macOS will not normally try to index read-only media.
In general, cameras require a certain structure of folders and files in order for the content to be reviewable in the camera. You will need to maintain that structure, including following naming conventions, if you expect to transfer files for in-camera review. In other words, whatever the original structure of files and folders is, maintain that exactly, and it should be readable in-camera.
If you aren't sure whether you're correctly maintaining the structure, then do a trial run with your spare SD card. If it works, great, you've confirmed what works. If it doesn't work, then you should explain exactly what you did, and folks here may be able to suggest other things to try.
If you don't have any spare SD cards at all, then it might be prudent to look in your camera's manual and find out what the largest capacity card is that was recommended at the time. Buy one of those, or something smaller.
I strongly suggest working through several trials with a spare unused SD card before attempting anything with a card containing valuable data. Always practice on something safe. Oh, and take notes on what works and what doesn't work.
FWIW, this is the same strategy as one would use when writing any storage media M on any digital device D. If it's a USB tape drive on a Raspberry Pi, or a CF card connected to an iPad, work things through with spare storage media, and try things to see what happens.