If you're specifically looking for features or functionalities available in older versions of the YouTube app, you might want to check out what's currently available on the YouTube website or through their official app on the App Store.

The YouTube app must already be linked to your Apple ID . Step-by-Step: Open the App Store on your iOS 12.5.7 device.

This is the most reliable method for non-technical users. It forces the App Store to offer the "last compatible version".

Apple allows users to download the last compatible version of an app if they have previously downloaded it.