If you are trying to upload hero images in your campaign and don't see the file upload dialog on clicking the "Upload Image" button, you are probably facing a known Mac OSX bug.
Due to this bug, file upload dialog across all websites on Chrome get disabled.
While it is not known exactly why this happens, there are some solutions that seem to work. The "FIX 1" mentioned in the article https://www.droidwin.com/fix-cannot-upload-files-via-chrome-in-macos/ does seem to fix the bug.
If your file uploading doesn't start working after applying fix mentioned in the above article, please do let us know.