The $PLUGINSDIR folder created by NSIS inherits the parent folder's permissions. This means (at least on my system) full control for SYSTEM, Administrators and the user. I'd like to remove the write access for the user to protect the libraries, which are copied to the folder and then loaded during installation. Is it possible to do it somehow?
$pluginsdir is restricted (only BUILTIN\Administrators can write) when the installer runs elevated. This restriction was first added in v2.51 and v3.0 in 2016.
Use the Access control plug-in if you need a custom ACL.