I have problems with installing the new remix beta plugin. After downloading, installing and restarting glyphs the following message appears when I want to activate the filter: "This RMX beta version has expired. Please check remix-tools.com for updates."
Somehow, the new beta has never been installed correctly.
Before the new beta was released the former version worked.
This is strange. When you double-clicked the RMX.glyphsFilter file, did it ask you whether to overwrite the existing one? It should also tell you the location where the filter is installed. Maybe you can open that folder and have a look there?
I never found the Library folder inside the user folder. Your hint with Open Scripts Folder opened the requested folder now. In the Finder window [username]/Library is marked as grey. A privileges problem, I guess.
I cleaned the mess in the Plugins folder and just re-installed RMX. Now everything is working fine again. Great!