Here is the solution.

Edit nano /etc/systemd/resolved.conf, add following lines.

DNS=1.1.1.1
FallbackDNS=8.8.8.8

Run following commands.

systemctl enable systemd-resolved.service
systemctl stop systemd-resolved.service
systemctl start systemd-resolved.service
systemctl status systemd-resolved.service

This will print the status of service

● systemd-resolved.service - Network Name Resolution
     Loaded: loaded (/lib/systemd/system/systemd-resolved.service; enabled; vendor preset: enabled)
     Active: active (running) since Mon 2024-04-22 14:24:30 CST; 3s ago
       Docs: man:systemd-resolved.service(8)
             man:org.freedesktop.resolve1(5)
             https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers
             https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients
   Main PID: 48211 (systemd-resolve)
     Status: "Processing requests..."
      Tasks: 1 (limit: 9488)
     Memory: 4.1M
        CPU: 115ms
     CGroup: /system.slice/systemd-resolved.service
             └─48211 /lib/systemd/systemd-resolved

Apr 22 14:24:30 aabbdde systemd[1]: Starting Network Name Resolution...
Apr 22 14:24:30 aabbdde systemd-resolved[48211]: Positive Trust Anchors:
Apr 22 14:24:30 aabbdde systemd-resolved[48211]: . IN DS 20326 8 2 e06d44b80b8f1d39a95c0b0d7c65d08458e880409bbc683457104237c7f8ec8d
Apr 22 14:24:30 aabbdde systemd-resolved[48211]: Negative trust anchors: 10.in-addr.arpa 16.172.in-addr.arpa 17.172.in-addr.arpa 18.172.in-addr.arpa 19.172.in-addr.arpa 20.172.in-addr.arpa 21.172.in-addr.arpa 22.172.in-addr.arpa 23.172.in-addr.arpa 24.172.in-addr.arpa 25.172.in-addr.>
Apr 22 14:24:30 aabbdde systemd-resolved[48211]: Using system hostname 'aabbdde'.
Apr 22 14:24:30 aabbdde systemd[1]: Started Network Name Resolution.

Now, problem solved.