Just for future reference, you can disable DNS management for specific groups [0].
You can find the option under "DNS > DNS Settings > Disable DNS management for these groups". Netbird will stop modifying the resolv.conf on those groups.
Can Netbird run the DNS resolver (so it can be used for the internal domain ONLY by systemd-resolved) but not alter the host's DNS settings?
It looks to me like the setting that tells Netbird to leave the system DNS alone is arbitrarily tied to the setting that causes it to run a resolver at all.
You can find the option under "DNS > DNS Settings > Disable DNS management for these groups". Netbird will stop modifying the resolv.conf on those groups.
[0] https://docs.netbird.io/manage/dns#4-dns-management-modes