The full version of ST-Sim runs on Microsoft Windows. To run ST-Sim on a Mac you will need some kind of virtual Windows software to be able to run ST-Sim. Most people use “Parallels”, although there are other options. Here is a link to an article about running windows applications on a Mac: https://www.howtogeek.com/187359/5-ways-to-run-windows-software-on-a-mac/
A user running on parallels on a Mac recently encountered an error whereby when they tried to open a library they received an error entitled “unable to open database file”. I helped them resolved this, which was related to the ssim library file being located on the Mac partition of their drive. If running on parallels, you should ensure that your data files are on the windows partition (in his case it was the C drive which in windows explorer was displayed alongside the windows icon).