We have Spectrum 21.2.12 installed on a CentOS8 server.
I can see Model Type Editor is greyed out in the Spectrum Control Panel so I can not launch it.
I also can not start it from the command line as the "mte" file is missing from the $SPECROOT/SS-Tools directory.
Spectrum 21.2.x
Re-run the Spectrum installer and make sure you select the 'Model Type Editor' in the components to be installed: