Always best to share some context. For example. where are you uploading the image to? A product? An asset? Files?
Are you able to upload one of the images somewhere else so the forum members can see it and - if needed - test?
What Shopify means here is that the image dimension exceed 20MP, not 20MB. Make sure the resolution of your image does not exceed this limit.
Let me know if that fixes it!
Has this been tackled meanwhile? Is there any arrangement? I have the very same issue, any place I need to transfer a picture (JPG, JPEG, PNG). Every around 1-1,5 MB and Shopify says the pictures terminate 20 MB. Where does that come from?