Here is a thing about OpenDNS you might not know. It actually has parental control feature that let you filter various domains based on category. They implemented by allowing you to enter your current IP address, and then all DNS requests from that IP address will run through the selected filter: https://signup.opendns.com/homefree/

One more thing. Mobile carrier often use CGNAT, which will put a bunch of customer behind the same set of public IP address. When you're behind a CGNAT, your request will appear to come from the same IP address like other customers of the same mobile carrier in that area.

What happened to you is someone in the same CGNAT enabled parental control on OpenDNS and registered the CGNAT's public IP address as their own. This result in everyone in the same network to have their DNS requests filtered according to that user's parental control settings.

You might need to wait until you got rotated into a new public IP address, or use a VPN. The real question is why your carrier use opendns in the first place.

Make sure the URL is using HTTPS:// not HTTP://

Select the bottom option "private DNS hostname" and enter either one.one.one.one or DNS.google.com

Yes, you have those enter a hostname not an IP. Not sure why but it works for me on my android phone.

Can you post an example of such a blocked site? And in which country are you?

There are two basic ways I can think of that you could still end up using OpenDNS without setting it as your DNS server in the private DNS settings. The first is simply if it's the default DNS that your ISP (in this case the phone company, since you mention you're not on WiFi) supplies. If you don't set a DNS server, then your system will obtain one at the same time it obtains an IP address via DHCP during the initial handshake with the ISP, because it needs to use something to translate website names into IP addresses. So if the ISP is configured to suggest OpenDNS, that'll still be what you'll use. You can override this by manually setting another DNS server. Note though that many DNS services (including a Google, if I recall correctly) use OpenDNS as a fallback setting, so if the main DNS site is down for some reason, you might still get OpenDNS results.

The other possibility is if have a VPN enabled, like Adguard or DNS66. These often affect DNS resolution as part of an effort to block ads. Again, manually setting a DNS, or disabling the VPN, should override this.

One last note is that there's a setting in Chrome that lets it bypass your DNS settings and use Google's own DNS for that app, so if you're using Chrome and Google's DNS server is down or doesn't have an entry for a particular site, that could still lead to OpenDNS being used for resolution. I haven't really found turning off that setting to work in getting Chrome to use my configured DNS, which is part of why I now use Firefox on Android, but in theory it should be possible to fix with "settings->privacy and security->secure DNS->use current provider," or with a custom configuration in the same setting, in Chrome, or by turning off secure DNS in the same spot.

Note that all these settings do have privacy implications, so it might be worth reading about those before mucking with any of them!

@WarmSoda use mullvad dns (free) or nextdns (freemium)

I think none of this has to do with Private DNS (which is what you found on the internet refers to).

Does the issue only happen on LTE or at home? My guess is that your DNS configuration on your home router or from you cellphone provider have been modified to use OpenDNS's (or any other DNS that cause an issue)

Also, could you provide a screenshot of your browser telling you the website isn't secure?

Try a different browser or check dns settings in your browser, I don't use firefox so I don't know if it has that setting. You can also use a vpn, it should override your dns settings. Proton vpn is free for the basic tier.

Try to enter one of these DNSes there.

94.140.14.14

94.140.15.15