How do I downgrade my iPhone from iOS 26 to iOS 18.5?

Unfortunately, you can’t downgrade an iPhone to iOS 18.5 once it’s been updated to iOS 26.

Apple only allows installing versions of iOS that are still being signed — and older versions like iOS 18.5 are no longer signed by Apple’s servers. That means even if you have an IPSW file, the installation will fail because the signature check won’t pass.

If iOS 26 feels unsatisfactory, the best thing you can do is:

1. Submit feedback to Apple here: https://apple.com/feedback/ – this helps improve future releases.
2. Check for upcoming updates under Settings › General › Software Update – Apple often fixes issues quickly with minor updates.
3. Restore your iPhone via Finder or iTunes if you think something went wrong during the update. This can sometimes improve performance.

Once Apple stops signing iOS 26 and releases a new version (like iOS 26.1), you can only move forward, not back.

If you just want your phone to feel faster or more stable again, a clean restore from backup usually helps a lot!