I have wasted the last 2.5 hours trying to see where I went wrong with my configuration and I just can't.
For the record, I am running OpenSuse Tumbleweed with Gnome, latest update for everything. Up to now I have been using AdGuard as my DNS resolver, but am now trying to switch to Mullvad but at this point I think I probably don't want to anymore. Reason being, I just can not get it to work for the life of me.
My system has NetworkManager installed so I go there, select my connected Wifi, and enter Mullvad's DNS address 194.242.2.4 in thr IPv4 section, then I go to check to see if it shows I am using their DNS and it Firefox AND Vivaldi give no internet connection errors. I go back to Adguard DNS and my internet is back working again. I go back to Mullvad, you guessed it, no internet once again. I even tried Cloudflare and Quad 9's DNS addresses and both of those worked as well but Mullvad's just does not want to work and I am going insane over it.
And no I can not edit resolv.conf through the terminal because NetworkManager will override it and no I don't want to delete NetworkManager. Any feedback would be appreciated.
Edit: I have Mullvad DNS on my phone and got it running with zero issues so this is more of a Linux problem than a Mullvad DNS problem I think.
Solution:
Open terminal and follow through
sudo zypper install systemd-network
sudo nano /etc/systemd/resolved.conf
Copy paste this into the file that you just opened and change the DNS to whichever DNS provider you are using.
[Resolve]
DNS=194.242.2.4 2a07:e340::4
FallbackDNS=194.242.2.2 2a07:e340::2
Domains=~.
DNSSEC=yes
DNSOverTLS=opportunistic
#MulticastDNS=no
#LLMNR=no
#Cache=yes
#CacheFromLocalhost=no
#DNSStubListener=no
#DNSStubListenerExtra=
#ReadEtcHosts=yes
#ResolveUnicastSingleLabel=no
Ctrl + O to write out and Ctrl + X to exit back to the terminal main page.
ln -sf ../run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
sudo systemctl start systemd-resolved
sudo systemctl enable systemd-resolved
sudo systemctl restart NetworkManager
Boom it should be working now.
You can edit resolv.conf and
# chattr +i resolv.confmakes the file immutable.
It's a kludge, and I'm not saying that it solves your DNS issue, but NM can't override the file.
How would I undo this process? I am considering testing this out but how would I make it overridable again just in case?
Edit, just tried it and added the DNSoverTLS=yes line and it did not seem to fix anything so unfortunately this isn't a solution but still a nice thing to know.
Another option is to remove it and symlink it to a static version of your choosing. I believe NM won't replace a symlink. You can just remove the symlink when you're done and it should go back to normal...I think.