If you move your iPhone SE to iOS 13.5.1 and you hate its performance, note that you can no longer downgrade to the previous version of iOS 13.
Apple has stopped signing on iOS 13.5 which means you can't use a loophole to drop your phone back in an effort to improve your device's performance.
If you really want to move your phone off iOS 13.5.1 you can move to Apple's latest iOS 13 beta. Betas are typically plagued with bugs, but there's a chance it improves your phone's performance.
If you're unfamiliar with the iOS downgrade process, take a look at our guide.