@Sampletekk In Inno Setup, the commoncf64 directory constant is used for 64-bit Common Files folder. So the below is the example for VST3 & AAX folder installation with Inno Setup.
Source: FolderPath\YOUR_PLUGIN.vst3; DestDir: "{commoncf64}\VST3\"; Components: VST364; Flags: ignoreversion
Source: FolderPath\YOUR_PLUGIN.aaxplugin\*.*; DestDir: {commoncf64}\Avid\Audio\Plug-Ins\YOUR_PLUGIN.aaxplugin\; Components: aax_64; Flags: ignoreversion recursesubdirs createallsubdirs