The better option is to configure DHCP to hand out the Pi-hole as your DNS server. If your router cannot do that, but you want to go deep enough to configure your home network with a Pi-hole, you should probably also invest in either a better router or OpenWRT on your current one to get a few more features.
Ideally, you do not run DNS on your router at all, and you also block outbound to 0.0.0.0:53 from anything _except_ the Pi-hole, so that there's no convenient way to get to an unblocked DNS by bypassing it.
DNS-over-HTTP is a bit harder to block, and of course malware could have an IP baked in and so bypass this entirely.
Ideally, you do not run DNS on your router at all, and you also block outbound to 0.0.0.0:53 from anything _except_ the Pi-hole, so that there's no convenient way to get to an unblocked DNS by bypassing it.
DNS-over-HTTP is a bit harder to block, and of course malware could have an IP baked in and so bypass this entirely.