Trevor Alyn - Stereozoom Lite

Stereozoom Lite is an iOS app that lets you:

Open side-by-side (parallel or cross-view) and Spatial photos from Photos, Files, the share sheet, or the clipboard
View any compatible SBS 3D photo in SBS Parallel, SBS Cross, Grayscale Anaglyph, and Dubois Anaglyph mode
Zoom and pan with two fingers
Use automatic alignment, or align by hand with a one-finger swipe
Swap sides
Rotate 180°
Flip the image horizontally
Use Aspect Ratio and Fit & Align controls
Realign misaligned images
Apply image effects and hue/saturation/brightness adjustments

After you adjust a photo, you can save it as a side-by-side JPEG or PNG, a Spatial photo, a grayscale anaglyph, a Dubois anaglyph, or an animated wiggle GIF. Your alignment, effects and color adjustments are baked into the saved file, and you can crop it to the area you've zoomed in on.