If you can't open JPG files even after that, consider resetting the app from the same menu. Doing so will remove all app data, effectively fixing issues caused by corrupt data. Open the JPG File ...

Photos can’t open this file because the format is unsupported ... sure the image or video is converted into common formats like JPG, PNG for images, and MP4 format for videos.

but you can use it to add a JPG to a document and then export that document as a PDF file. Although it can't open PDF files, OpenOffice can save valid PDF files that you can later edit in Adobe ...

Alternatively, with the extensions installed, you can also open your HEIC photo in Paint and navigate to File > Save as > JPEG picture to do the same thing. For every roadblock, there's a Mac utility.