Sorry to read you are having this issue. However you are saving it is not actually saving as a jpg properly. You can only upload jpgs or png files here. You will need to open them in editing software. and then save it, or a copy, as a jpg.
You can get this issue with SD card saves
In the latest phone update, it was suddenly decided by the phone company to default to saving pictures as HEIC files that saved space instead of jpgs.
In an iPhone you can change this in camera settings. Under format choose COMPATIBLE (NOT High efficiency) then future images will be saved as jpg.