It’s not hard to setup a pi as a backup DNS on your local network, but how I’ve setup a few friends who have limited hardware is to have the primary DNS as the local adguard and the secondary DNS as adguards public adblock DNS
That way if the local falls over, you still get some as ad blocking from their public one. If your setup allows it, they also have a public doh and dot encrypted dns for a bit of privacy
Many years ago I had a Facebook account under my real name, and they blocked it and told me to verify … I did everything they asked and they wouldn’t accept it… I recreated it under a fake name (very obvious it’s fake since it uses a celeb name) and have been using it for messaging a couple of friends for like a decade now with no issue