First, uninstall all FNC related components. Search on your system for all remaining DCU, BPL, DCP files related to FNC and remove them manually. Start the IDE and see if it starts normal. Then install TMS FNC Core, TMS FNC UI Pack and see if the components are shown. If they are not shown then it's unclear what exactly is going on. There is one thing you can do and check the registry for disabled packages.
Computer\HKEY_CURRENT_USER\SOFTWARE\Embarcadero\BDS\21.0\Disabled Packages