Why Do My Photos Open in the Wrong App?
Usually a file association, sometimes a format your system does not really support. Here is how to tell which.
On Windows, right-click a photo, choose Open with, then Choose another app, and tick Always use this app. On a Mac, select the file, press Command-I, change Open with, then click Change All.
If the photo will not open properly in anything, the format may be the issue rather than the association. HEIC files from an iPhone need extra support on Windows and on many Linux systems, and without it they simply fail.
Converting to JPG solves that permanently, because JPG opens everywhere. Takeout JSON Metadata Fixer converts HEIC to JPG while keeping the date, the GPS and the correct rotation, which naive converters lose.