Just be aware that browser vendors are increasingly pushing for DoH, similar things are likely to appear on your phones and entertainment devices as well, so you are pretty much on borrowed time with plain DNS hijacking.
The LuCI connections page relies on the original unmodified IP protocol headers.
DNS hijacking uses firewall redirects to modify the destination.
You can also check the packet and traffic counters for the redirects on the firewall status page.
Although you cannot redirect it, you can block those TCP/443 DoH servers in firewall, as many as you find, and there are lists on the internet. You can block TCP/853 DoT as well. Just make sure you don't block the server you use.
I'm doing that in my main home router (MikroTik) and it's automatically updated with a script, also dst-nat'ting port tcp/udp/53 (normal dns) to my own server.