HEIC and HEIF are image formats used by Apple iOS devices.
At this time, if you select one of these file formats to upload to Dash from a mobile browser such as Safari or Chrome, the browser will upload the file in JPG format. This appears to be an iOS decision that we aren't able to control.
If you do want to preserve these file formats when uploading into Dash, you will need to:
Save the photo to the Files app (Share icon > Save to Files)
In Dash click Upload > "Choose Files" and locate the file