When prompted with "Download an older version of this app?", tap .

Change their values from the current version (e.g., 17.39.4 ) to a newer one like 19.02.3 . and restart your device (SpringBoard). Method 3: The Web Browser Alternative (Easiest)

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.

If YouTube isn't in your history, log in to your Apple ID on a newer device (iOS 14+) and download it there first. It will then appear in your "Purchased" list on the older device.

If you want to avoid jailbreaking and the app remains buggy, using the mobile browser is the most stable "exclusive" way to watch without restrictions.