Problem
The OBS Flatpak is the recommended way for installing on Linux.
At least from the Terminal, finding and installing plugins is easy:
flatpak search obsproject
But to use NoiseTorch (COPR), which allows to mute background noise from audio input, you need to use Pipewire input.
Pipewire allows way more things like this, processing an input stream (here the audio) in some app (here NoiseTorch), sending the output to another one (here OBS) etc.
Cause
OBS has no Pipewire input by default for some reason, and the plugin is not packaged as a Flatpak.
To solve this, we need to manually install the plugin.
Workaround
Create the plugin directory:
mkdir -p ~/.var/app/com.obsproject.Studio/config/obs-studio/plugins
xdg-open ~/.var/app/com.obsproject.Studio/config/obs-studio/plugins
Download the latest release of the Pipewire Plugin and unpack it in this directory.
Now restart OBS and the new input sources should appear.
NoiseTorch
Download it here and install following their recommendations.
Better Solution
Packing the plugin as a Flatpak runtime