/etc/systemd/resolved.conf.d/fallback_dns.conf
[Resolve] FallbackDNS=1.1.1.1 1.0.0.1 2606:4700:4700::1111 2606:4700:4700::1001
/etc/systemd/timesyncd.conf
[Time] FallbackNTP=time.cloudflare.com
/etc/systemd/resolved.conf.d/fallback_dns.conf
The same with NTP:/etc/systemd/timesyncd.conf