Not at all, since the DNS traffic to 1.1.1.1 is still unencrypted and unauthenticated (unless you're using DNSCrypt or similar, or the domain you're looking up uses DNSSEC and you're using a validating resolver).
Correct me if I'm wrong, but I think the ios app has dns over https or dns over tls enabled.
No idea; I took your comment to refer to using 1.1.1.1 for DNS in general, since it didn't mention any app.