Emulator

Billiard26 wrote in #note-1:

The NetPlay host can assign multiple ports to each Dolphin client with the NetPlay window's Assign Controller Ports button.

If you are trying to use your local port 2, without using local port 1, yes, that is purposely not possible.
To make the Assign Controller Ports window far less confusing the local ports are automatically allocated sequentially.

Is there a specific thing you are trying to do that isn't working?

I might not be able to word my issue any better so I'll just tell what I experienced:

I wanted to play with a friend using Dolphin's NetPlay;

I was using a GameCube Controller connected to a Mayflash GC Adapter set to Wii U/NS and he was just using a Standard Controller;

I connected to his lobby, so I was assigned Port 2 automatically;

When he started the game, I noticed I couldn't move anything, like my controller wasn't even plugged in, even though it worked just fine when playing by myself just a moment ago;

we then quit the game, he assigned me as Port 1 and he as Port 2, after that my controller worked;

I tried being the Host instead to see if there was any difference; it worked normally if I was Port 1, but if I tried being Port 2 it didn't work;

I did try changing the physical controller ports on the adapter to see if there was any difference, nothing changed, I tried all 4 ports;

I then changed the mode on the adapter to PC, and configured my controller as a "Standard Controller";

everything worked just fine, confirming it's possibly just an issue when using an official GC adapter;

I then tried using version 2606a (stable), and there wasn't any issues;

after searching for the first problematic version I found it was 2606-110, with version 2606-108 being the last working as intended version.

Configure port 1 and plug your controller into the physical port 1 of the adapter, regardless of which port is assigned to you by the NetPlay host.
This is how it's intended to work, so you don't need to constantly change port settings.
Everyone just uses port 1.

Possibly GCAdapter + NetPlay was broken in 2606-110 https://github.com/dolphin-emu/dolphin/pull/14619.
I still need to investigate.

To add to the explained issue, these pictures are what the emulator does once the Netplay game starts:

This is my picture. It does not match my settings, in which I have the GC Adapter in Port 1 (below).

These are my settings outside of Netplay. Notice how the Standard Controller is set to Port 2.

This image was my host's, in which the outcome is reversed from the first image. As with mine, theirs does not match their settings (all 4 ports are set to GC Adapter).

Edited (I pasted the wrong links).

This should be fixed by https://github.com/dolphin-emu/dolphin/pull/14896
A windows build is here if you could please test. https://dl.dolphin-emu.org/prs/da/84/pr-14896-dolphin-latest-x64.7z