Firewall wouldn't be necessary with GrapheneOS. There's a network toggle which you can use to completely cut off internet access for an app. As for the downside

Firewall wouldn't be necessary with GrapheneOS. There's a network toggle which you can use to completely cut off internet access for an app. As for the downsides, I would say close to zero. It feels just like a stock OS, without any kind of bloatware and a lot more secure