If your black spots appear consistently in the same location, you probably have dust particles on your sensor. This is a common problem for DSLRs and mirrorless cameras with interchangeable lenses.
When you change a lens or have your camera body open dust can enter the body and adhere to your sensor. These dust particles will block light that your sensor needs in order to give you a complete picture.
A good way to check is to get your lens out of focus and take a picture of the sky with a small aperture. Once you have this photo, you are able to zoom in and start looking around for spots.
We recommend getting your sensor cleaned every year, or whenever you start to see spots.
We offer sensor cleanings at The Camera Company. https://cameracompany.com/services/sensor-cleaning