Start Here: What Usually Goes Wrong
Almost every beta problem falls into one of four groups. The beta never appears — nearly always an Apple Account mismatch, where the account you enrolled with is not the one signed into the device. The install stalls — usually free space, since the installer wants far more room than the download size implies. Everything got slower or the battery collapsed — normally the first-week reindexing that resolves on its own by day four. Something is broken and you want out — which means either turning off Beta Updates and waiting, or restoring the previous version from a backup you made beforehand.
The last group is the one worth planning for before you install anything. An iCloud backup taken while running a beta cannot be restored onto the older release, so the only reliable route back is an archived encrypted backup made on your computer before you enrol. Every downgrade guide here assumes you have one, because without it a restore means starting from an empty device.
One thing none of these fixes involves is a profile. Apple removed configuration profiles from the beta process in 2023, so if a troubleshooting page elsewhere tells you to delete or reinstall a beta profile, it is describing a version of iOS that has not shipped in years. The current controls all live in Settings → General → Software Update → Beta Updates.
Downgrade
Beta program
Troubleshooting
Explainers
Still stuck? The FAQs cover the basics, your device's compatibility page covers model-specific behaviour, and each install guide has troubleshooting specific to that device.