I have been using GrapheneOS now for 8 month and its been quite a smooth ride. The biggest worry I had was flashing it onto a brand new Pixel phone I had just bought. Everything else works fine though. Currently using 3 (german) banking apps and I haven't had a single issue. Also still using Google apps like camera and maps. Also Gboard as the default GrapheneOS keyboard is a bit uncomfortable. Really nice that you can just remove the network permissions and it works like a charm