This is what worked for me, based on Manga's instructions (updated two Macs - a MacBook Pro and an iMac, both running Mojave):
1. Make sure Island Rum is updated to version 082220191. Shut it down.
2. Install Homebrew and Wine via your Terminal (located under Applications/Utilities. You need to run it as the admin for your Mac as it will ask you for your Mac password). Follow the instructions at http://brew.sh first, and after Homebrew installs, run "brew install wine" in Terminal.
3. When all that is done (take a few minutes), re- open Island Rum. You should see some progress bars updating and installing. If you don't, open the first drop-down menu (the palm tree) and select RESCAN. (You could probably rescan either way, just to double-check). When that's done, close Island Rum and re-start your Mac.
4. Upon re-boot, re-open Island Rum, make sure "Homecoming 64-bit" is selected and proceed as you normally have done.
That should do it! (I hope) 🙂