Can I downgrade from iOS 26 beta to iOS 18 without resetting my iPhone?

You can't uninstall iOS 26 beta to use iOS 18 without resetting your iPhone. As an operating system, iOS is your iPhone's bedrock software. Simply removing a beta profile or deselecting beta updates won't revert the changes you made when upgrading to iOS 26. 

iOS updates to the latest version, and if you have beta updates enabled, those will also be included. If you want to downgrade from iOS 26 to the stable public version of iOS 18, you'll need to restore your iPhone.

Also: Some apps are battery vampires - how to root them out and shut them down

This is why you should always back up your devicebeforeinstalling a beta version of iOS -- not after. Backups made on a beta version are generally incompatible with older available software versions and will result in lost data.

Do I need to use a computer to uninstall iOS 26 beta?

You will need a computer to uninstall iOS 26 developer beta, either a Mac or a Windows computer with iTunes. If you choose to reset your iPhone from within its Settings without a computer, it will just delete your data but maintain the iOS 26 version already installed. 

Putting your device in Recovery Mode lets you use the computer to erase it and install the latest public iOS version.

What problems does the iOS 26 developer beta have?

iOS 26 developer beta is no more buggy and unstable than other developer beta versions of software. Any time you install a beta version of a software, either a public beta or a more exclusive developer beta, you're installing pre-release software that hasn't been perfected. 

Using a developer beta on an iPhone may present diminished battery life, unreliable app performance, suddenly unresponsive screens or applications, glitching, and overall sluggishness. However, these are expected bugs that developers and users report to Apple so the company can correct them before the stable release of the software.