已解决:
cat /etc/resolv.conf
resolv.conf(5) file generated by tailscale # For more info, see https://tailscale.com/s/resolvconf-overwrite # DO NOT EDIT THIS FILE BY HAND -- CHANGES WILL BE OVERWRITTEN nameserver 100.100.100.100 search tail96c7e.ts.net
卸载tailscale后,/etc/resolv.conf仍被tailscale占用,web界面配置DNS没有生效。
sudo mv /etc/resolv.conf /etc/resolv.conf.bak
echo "nameserver 223.5.5.5" | sudo tee /etc/resolv.conf
echo "nameserver 119.29.29.29" | sudo tee -a /etc/resolv.conf
手动更新DNS,恢复正常。