Is MDM profile required for local custom VPN for content filtering

I am trying to have a local VPN for content filtering for an iOS app.

Using a VPN for content filtering is not a recommended practice. See TN3120 Expected use cases for Network Extension packet tunnel providers for the reasons why. Instead it is recommended to use one of the Content Filtering APIs on iOS, in which case, yes, you will need to be setup on a supervised device unless you are using the Screen Time APIs. Here's an excerpt from the Technote above:

"There are two ways to deploy a content filter on iOS. In a managed environment, use MDM to deploy a content filter to supervised devices. In an unmanaged environment, deploy your content filter as part of a Screen Time app."

Thanks for your response. But i want to put in this way.

We did not intent to do content filtering locally, but with local proxy server (VPN) we will be configuring the DNS settings (DOH) in the network extension. The filtering is done on the DNS traffic in the cloud or remote.

We don't want to just use DNS settings as those are supported from IOS 14.

Could you please share some reference on Screen time app. What are the use cases and capabilities.