When i'm on mobile data I can barely get it to send imessage. I have a Pi4 right now on which I plan to install it (diet pi seems to have really easy setup for wire guard since i had trouble on the raspios aarch64 lite image, i think headers were missing) but for now nextdns seems to be okay. NextDNS has their own app for iOS but I sometimes have trouble on that too so i just switch DNS and see what works best. The ISP DNS are definitely worse than anything.