Let me show you how to settings PrivateDNS on mobile :
Head over to Setting -> Connection & Sharing -> PrivateDNS
(Copy one of services below)
Google DNS : dns.google (not recom)
Quad9 : dns.quad9.net
Open DNS : 208.67.222.222
NextDNS : 45.90.28.0
Comodo Secure : 8.26.56.26
OpenNIC : 192.95.54.3
Adguard : dns.adguard.com
Once u copied from above, click OK then you'll never see any ads. Ever. [these are for Android btw]
** Problem might arise when u tried to click ads from email that u subscribe from, the doubleclick.ads might not works and you'll never get to the linked products from your email.
U can always revert back using default DNS or even off DNS. your choice really.