Did you follow the guide from here
Also, this is the latest script to install. Its the one I use and have no problems installing on an RPI3B
If/When the script says joy2pi is missing,d on’t worry about that. Thats installed in the intial install and isn’t really needed for the initial installation
The install script should automatically download all need libraries and any extras needed for correct installation
Also, if you are install RetroSMC on the OSMC VERO 4K that isn’t supported at present, but apparently does work but more effort is needed to get it to install correctly