Add the following repository in Cydia: http://cydia.skyglow.es/ . Install the tweak.
The simplest way to get a compatible version without external files is to leverage your Apple ID's history. This works if you have previously downloaded YouTube on any Apple device. on your iOS 9.3.5 device. Navigate to the Purchased tab at the bottom menu. Search for "YouTube" in your list of apps. Tap the Cloud Icon . youtube ipa for ios 935 exclusive
Download a legacy YouTube version (like v2.2.0) from the TubeRepair Website . Add the following repository in Cydia: http://cydia