how to downgrade from ios 14.5 beta 1 to stable ios 14.4?

Read ALL of the instructions that were posted: How to uninstall iOS beta software - Apple Support

No, it won’t downgrade. After you remove the profile you will have to restore your phone using iTunes, which will install the current version, iOS 14.4. You will not be able to restore a backup made with the beta version; if you saved a 14.4 or earlier version as a backup you can restore that.

Remove the public beta by deleting the beta profile

Go to Settings > General, and tap Profiles & Device Management. Tap the iOS Beta Software Profile. Tap Remove Profile, then restart your device.

How to uninstall iOS beta software - Apple Support

I recommend that you ask this question exactly as you have stated in a Google Search Bar. You will get plenty of results and methods just to do that.

Here, in this forum, we cannot discuss beta iOS versions or applications. IOS BETA 14.5 Developer Version is released and you appear to have it. You must be a developer and you should have the information about where to post Beta related questions.

Axel F.

This is not the right forum to discuss beta

When you experience an issue or something does not work as expected in beta, send your feedback directly to Apple with Feedback Assistant.

I did that and it didn’t downgrade

I uninstalled the profile but I am still on 14.5.