Date: 2023feb4 OS: Linux Q. systemd-resolved[]: Using degraded feature set UDP instead of UDP+EDNS0 for DNS server n.n.n.n A. For me it was saying that because DNSOverTLS wasn't available on that server. So in file /etc/systemd/resolved.conf I changed DNSOverTLS from yes to opportunistic

[Resolve] DNSOverTLS=opportunistic

Then:

systemctl restart systemd-resolved.service

Now it doesn't complain if a server doesn't have DNSoverTLS. You can do:

resolvectl status

To get its status