What do you do if you want to find the IP address of an instance, but incus list does not give you one?
If that's the case then it means there's no networking configured for the container or inside it. The image you're using may not come with DHCP enabled or networking at all.
I often just find the IP of the container and then ssh in as that feels natural, but perhaps I am cutting against the grain here.
You are. You aren't supposed to SSH into a container... it's just a waste of time. Simply run:
lxc exec container-name bash # or sh depending on the distro
And you'll inside the container much faster and without wasting resources.