Even if you install an older version, Google often blocks it with a "Update Required" popup that can't be bypassed. If your device is jailbroken, you can spoof your version number to trick the app. Open (available via Cydia).
Navigate to: /var/containers/Bundle/Application/YouTube/YouTube.app/ . Find and open the file. install youtube ios 1257 exclusive
Locate the strings CFBundleShortVersionString and CFBundleVersion . Even if you install an older version, Google
When prompted with "Download an older version of this app?", tap . When prompted with "Download an older version of this app
This is the most reliable official method. If you have ever downloaded YouTube on your Apple ID before, you can download a "last compatible version." Open the on your iOS 12.5.7 device. Tap on your Profile icon in the top right corner. Select Purchased (or "My Purchases"). Search for YouTube in this list. Tap the Cloud icon with the downward arrow.