Mullvad is shutting down their public DNS. ref: https://mullvad.net/en/blog/shutting-down-our-public-encrypted-dns-servers-and-sponsoring-quad9-instead
To-do
Perhaps use overlay for /etc for speedup
system.etc.overlay.enable = true;
Performance for mini pc
security.pam.loginLimits = [
{ domain = "@users"; item = "rtprio"; type = "-"; value = 1; }
];