I was troubleshooting why my iPhone 7 Plus with iOS 13.1.3 is not validating my broken dnssec domain.
What I found is:
Chrome, App Store, Safari, etc. all of this app’s ignore 188.8.131.52 app and all dns traffic go to my default resolvers (from dhcp). All I checked on my router with tcpdump and it confirms. Same behavior is on cellular network.
ISC Dig see 184.108.40.206 resolvers in iPhone and use it correctly.
I had same iPhone 7 Plus (factory settings) with same iOS 13.1.3 and it was same.