Need to put a copy of the “,ny” file in the Audacity plug-ins folder, its location in Windows is …
Users\<username>\AppData\Roaming\audacity\Plug-Ins
NB: “AppData” is a hidden folder, so could currently be invisible to you.
Yes they’re different: “RMS normalize” is another Nyquist (.ny) plugin,
see … RMS Normalize
Audcaity 2.4.1 comes with RMS Normalization installed …
Loudness Normalization - Audacity Manual