resolv.conf is the configuration file for DNS resolvers for all Linux distributions, including Debian, Mint, Ubuntu, RedHat, CentOS, etc. Usually we change the DNS resolvers list by editing resolv.conf. However, depends on your dhcp client configuration, resolv.conf may be rewrite after reboot. Without deep Linux experience, setting customs DNS servers on Linux maybe time consuming. But one thing we can do is make /etc/resolv.conf immutable to other program after you changed it. This will be the easier setup with no side effects on system.
Below example we will set DNS resolver to 18.104.22.168. (22.214.171.124 is a privacy-first consumer DNS service provided by Cloudflare.)
sudo echo 'nameserver 126.96.36.199' > /etc/resolv.conf
Run the chattr +i command to sets the immutable filesystem attribute on resolv.conf, so it can’t be modified any anyone else.
sudo chattr +i /etc/resolv.conf
Reboot your system and test if your change to DNS server succeed. You can test it via DNS leak test. If you want to make change to resolv.conf again, you need to remove the attribute.
sudo chattr -i /etc/resolv.conf
Google Public DNS 188.8.131.52 / 2001:4860:4860::8888 184.108.40.206 / 2001:4860:4860::8844
OpenDNS 220.127.116.11 / 2620:0:ccc::2 18.104.22.168 / 2620:0:ccd::2
Comodo Secure DNS 22.214.171.124 126.96.36.199
Norton ConnectSafe 188.8.131.52 184.108.40.206
Level 3: 220.127.116.11 18.104.22.168
Verisign Public DNS 22.214.171.124 126.96.36.199
DNS.WATCH 188.8.131.52 184.108.40.206 2001:1608:10:25::1c04:b12f 2001:1608:10:25::9249:d69b
AdGuard Default 220.127.116.11 18.104.22.168 2a00:5a60::ad1:0ff 2a00:5a60::ad2:0ff
Family protection 22.214.171.124 126.96.36.199 2a00:5a60::bad1:0ff 2a00:5a60::bad2:0ff
Quad9 188.8.131.52 184.108.40.206 2620:fe::fe 2620:fe::10
Cloudflare DNS Resolver 220.127.116.11 18.104.22.168 2606:4700:4700::1111 2606:4700:4700::1001
CleanBrowsing Family Filter 22.214.171.124 126.96.36.199 2a0d:2a00:1:: 2a0d:2a00:2::