e.g. Quad9 as an example. The preset server does not fill in 853 for the port number.
I will admit I got my AX86U Pro and flashed Merlin before even seeing if this was an option on stock so apologies. If it is maybe a nice little feature to add into Merlin?
The port is included in the preset so no need to set it manually. If it wasn't DoT wouldn't work properly. I like it like this - no chance of messing it up.
I use the quad9 presets and I'm not leaking dns anywhere.