Suppose you subscribed to many YouTube channels. How do you unsubscribe from all deleted or terminated Youtube channels at once without going through each one of them?
Here's a way to unsubscribe from all YouTube channels at once. Go to your subscription manager page and copy this code into your browser's address bar, then press Enter:
I've tested it in Chrome but it should work in other browsers, too. Basically what it does is search through all the buttons on the page, find the ones that are used for unsubscribing from channels, removes the setting to ask for confirmation when you unsubscribe, then it unsubscribes from each one.