One of the reasons I went out and bought the Canon R100 was so that I could have a higher resolution camera than my aging EOS 400D. The 400D did 3888 x 2929 10MB images, whilst the Canon R100 did 6000 x 4000 24MB images.
I would import my photographs from the 400D onto the Mac into Photos using an USB cable. It would import the full size images.
One of there features of the R100 is to use WiFi to connect the camera. There was a Mac app, but I decided to use the app for the iPhone. The app would import the images from the camera and then save them to Photos on the iPhone, which then would upload them to iCloud so I could access them on the Mac if I needed to. I thought I had cracked that workflow.
By chance, I worked out that my camera was exporting images to the iPhone at a reduced resolution, way reduced. It was importing them at 1620 x 1080 rather than 6000 x 4000. Great for Instagram or Facebook, but not so good for full size editing.
On a recent visit to Glastonbury Tor I hadn’t deleted the images from the SD card so could re-import them at the correct resolution. You can compare the two images here.
This is the reduced image.
This is the original image.
You can click the images to see them full size.
In addition here is a zoomed in comparison of the two images, you can see the difference in resolution between the two images.

I did not realise that this was happening, so unfortunately, some of my first full resolution photographs from the R100 were lost. I had assumed they were transferring at full resolution, and I deleted them from the SD card on the camera.
I have changed the settings on the camera and I am now thinking about keeping the images on the SD card as a backup.
It was frustrating, so much so, that I am now thinking about going out again and retaking the photographs I had taken with the R100.