Iphone fails on some wifi

[oscy]

I have had the cloudflare 1.1.1.1 https installed on my iphone for some time.
I have lately noticed that on some wifi networks I can connect to the wifi however I don't get any internet connection.

Tried just about every setting in both router and phone to no avail. I realized that everything would start working if I enable VPN which got me thinking about the DNS profile (figure this gets overriden by VPN).
So I finally tried removing the profile on my iphone and the internet on the wifi instantly started working.
Reinstalled the profile and the internet goes down again. Tried installing the Google HTTPS and same problem.

I have been using the signed versions.
I am on iPhone 15 Pro with iOS 18.0.1

The most frustrating part is that the phone doesn't understand it doesn't get internet (it's almost like it does get at ultra slow speed) so no back up kicks in, I realize now that there have been many times I have thought wifi is bad when this probably all comes down to the profile somehow blocking.

[realyukii]

Is it possible for iphone to set dns server on cellular data without jailbreak it?

[realyukii]

Nevermind, found the answer on stackexchange