The guides below can't be used to stream DS games, DSiWare, and GBA games. You will need a hardware capture card to do that.
This only works for New 3DS. If you absolutely want a method for Old 3DS, there is HzMod. Keep in mind that performance is still very bad and it is not intended for practical use.
This page will show you how to stream your New 3DS console's screens to your computer over WiFi.
Your console and your computer need to be on the same network.
Streaming audio over WiFi currently isn't possible, you will need to use an AUX cable and a device with Line In to receive audio.
If you have a poor connection, you may not get the best results.
Finding your Console's IP
You'll need to know the local IP address of your 3DS later, so it's a good idea to find it now.
Start the Homebrew Launcher
Press Y
Launch FBI
Select "Remote Install"
Select "Receive URLs over the network"
Open Rosalina with Left Shoulder+↓+Select
Select "Debugger options..."
Select "Enable debugger"
Press B to continue
Find the IP address in the top right corner
Recommended: Select "Disable debugger"
Streaming with NTR+Snickerstream (recommended)
At the time of writing this, BootNTR Selector is not compatible with the latest standard release of Luma3DS. To combat this, we will be using a custom build with support for BootNTR.
Your console's screens should now be streamed to your computer
Using Line In to Receive Audio
What You Need
A 3.5mm to 3.5mm audio cable
An audio in (line in or microphone in) port on your computer
Some computers have a single "headphone" port that can be used for both audio output and input. To use one of these, you will need a Y splitter
How to use
Connect your 3DS to your computer's audio input port with a 3.5mm to 3.5mm audio cable
Pipe the audio from your audio input port into the software you intend to use
The exact steps will depend on the software you're using
If you are recording or streaming your game using OBS, add a new audio capture source
If you are streaming your game via a service such as Discord, you will need to use software such as Voicemeeter to mix your microphone and 3DS audio inputs together
If you do not wish to speak while streaming, simply point the app at the 3DS's audio device