https://askubuntu.com/questions/2219/how-do-i-clear-the-dns-cache

Ubuntu 17.04 and higher (18.04)

From Ubuntu 17.04 and onwards, systemd-resolve is used for DNS. You can flush systemd's caches like so:

sudo systemd-resolve --flush-caches

Ubuntu 22.04 and higher

sudo resolvectl flush-caches