Where should I configure DNS in Debian 11?

I'm using Debian 11 (Bullseye). I'd like to use a different DNS server. I found the file /etc/resolv.conf. It looks like this (by default):

nameserver 192.168.1.1
nameserver 1.1.1.1
nameserver 8.8.8.8

Fair enough default. Use the local router/gateways DNS, then Cloudflare, followed by Google's DNS. There is a second file, too, though - /etc/network/interfaces. For me, where is what it looks like by default (I'm using DHCP)

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
allow-hotplug enp4s0f0
iface enp4s0f0 inet dhcp

In that file, I can set my preferred DNS there by saying this, if I wanted to use, say, [quad9](https://www.quad9.net/) for my DNS.

dns-nameservers 9.9.9.9

So, if I'd like to change my DNS server, which file do I need to edit? Just one? Both?