Open the Camera app
Tap the front-facing camera icon
Tap the arrow or chevron at the top of the screen
Tap the Mirror Front Camera option
Turn Mirror Front Camera on
Open the photo you want to mirror in the Photos app
Tap Edit
Tap the Crop icon
Tap the Flip icon
Tap Done
Open the Shortcuts app
Tap the plus icon to create a new shortcut
Add the Resize Image or Rotate Image action if needed
Save the shortcut
Run the shortcut on the photo to mirror it