As of the moment, the only way to avoid getting booted offline is to not join random parties, don't reply/send messages, and don't play Peer-to-Peer connection games (Fortnite isn't P2P, so you shouldn't have to worry about that). If you'd wanna take it
a step forward, you can try connecting a VPN through your Xbox. The downside to this though is a computer with an Ethernet port is required, and preferably a VPN without a data cap. You can find a guide
here on how to do this for yourself.
