[tcauduro]

That's what the built-in shortcut app is for. Have it open the photo on run. Add it to your home screen or lock screen as needed.

[kodapoda]

That's a great idea! I only recently started using shortcuts and haven't yet developed the habit of solving simple tasks with them.

Edit: works very well. Created a shortcut that opens a specific file from Files, and added it to the home screen with a custom icon.