How Do I Open An .msi File On An iMac?
My games are way old school (UO & The Realm). so Windows-based.
How do I get them to run on a Mac?
iMac Line (2012 and Later)
Unless the game developer has released a 64-bit Mac version of these games, that is compatible with Catalina, you will have to run Windows 10 in Boot Camp (best for games performance). You will need a Windows 10 license for this.
Once you have Windows installed in Boot Camp, you boot into Windows and install that Microsoft Windows only .msi installer. The .msi installer file is useless on the Mac.