As always you should start with the tools available in the Spout release. Do the demo sender and recever work together? Do you see the demo sender in OBS? Do you receive VtubeStudio in the demo receiver? SpoutSettings has help and diagnistics that will help to trace the issue.
That’s a good start if you can receive VtubeStudio.
The purpose of the demo sender is to simply show something in a receiver. You should be able to receive it with the demo receiver and also with OBS. That will show whether the OBS side is working or not.
In SpoutSettings, just click “Reset” for the default settings and “OK” to save them.
In that case it appears to be isolated to OBS. I would suggest to re-install the OBS Spout plugin. If that doesn’t help, you might get help from the OffWorld Live discord group.