If you're missing NDI in OBS, the first thing to try is to run OBS as an administrator, because this immediately worked for me to fix it. I'm assuming you've already downloaded the NDI runtime or the NDI tools, which is what lets you send your screen from one PC to another. I did all of that and it still wasn't working, and it took me quite a while to figure out that the missing piece was simply running OBS with administrator privileges.
The fix: run OBS as an administrator
What I needed to do on OBS was right-click it and then click on Run as administrator. There seems to be some error going on with the graphics provisioning if you're not running as an admin. So once I clicked Run as administrator, everything worked and the NDI source showed up.
Make OBS always launch as an administrator
What you can also do is set OBS to run as an administrator every time. Right-click the OBS shortcut and go into Properties, then go into the Advanced options, and from there you can check Run as an administrator. You can do this on the shortcut for any program, including OBS. After that, by default it will launch OBS as an administrator, which is how I run OBS now.
If you found this helpful, you might also like my 2026 OBS settings for recording and streaming, and I share more of my streaming and YouTube workflow in my YouTube Coaching playlist.