There are three issues in recent versions of OS X that cause problems for Mini vMac.
Quick Fix : run “xattr -cr <Path to Mini vMac>” in the terminal.
(step by step instructions below)
Further explanation:
Starting with macOS 10.14.5, Apple wants software to be “notarized”, which involves sending it off to Apple for their computers to inspect and sign it. This is fundamentally incompatible with the Mini vMac Variations Service (which needs to finish in a few seconds), and is anyway disturbing. Fortunately, for now at least, using the xattr command will allow Mini vMac to run without notarization.
A second issue is caused by Path Randomization, added in macOS Sierra (10.12). If an application that Apple thinks is trustworthy is bundled together with malicious library code in the same folder, the malicious code may be run by the application. The silly way that Apple has chosen to prevent this is to in effect move the application somewhere else before running it, so it can’t find the library code. It can’t find anything else in the application’s folder either, which is a problem for Mini vMac, which looks for things in its folder, such as the ROM image file. One work around is to put the image in one of the other places that Mini vMac looks, as described in the ROM section of the Emulated Hardware Reference. Another option is to tell macOS not to do Path Randomization for Mini vMac, using the xattr command, as described in more detail below.
The other issue is caused by Gatekeeper, added in OS X Mountain Lion (10.8). By default, the operating system will refuse to run applications downloaded from the internet, unless Apple considers it trustworthy (because it is digitally signed by a developer registered with Apple). Gatekeeper is in some ways a good idea, but some people consider it as one step along the way to making OS X like iOS, where no software can be installed without Apple's permission, and emulators are forbidden, including Mini vMac. So I decline to participate, and Mini vMac is not signed with an Apple Developer ID. One way to override Gatekeeper, giving an application permission to run, is to hold down the control key and click on its icon (or right click) to get a contextual menu, then choose the Open item, and in the warning dialog that comes up click on the Open button. (This only needs to be done the first time Mini vMac is run.) Another option is to use the xattr command. update - Mini vMac has been signed with a Developer ID for a while, but xattr is now needed again because of notarization.
* From the Finder, choose the “Utilities” from the “Go” menu.
* Find the “Terminal” application (in the “Utilities” folder just opened), and launch it.
* Type “xattr -cr ” (not including the quotes, but including the trailing space), into the Terminal window that has just opened.
* Drag the icon of the Mini vMac application into the terminal window. (This should paste in the path string.) The result should look something like:
xattr -cr /Volumes/rd/Mini\ vMac.app
* Press the return key to execute the command. (This clears all extended attributes of all files in this application bundle.)
* You should now be able to launch Mini vMac without interference from Gatekeeper and Path Randomization.
warning: You should only do this for applications that you have reason to trust. Please only download Mini vMac from pages on “www.gryphel.com”. It would also be to good to check the md5 checksum and the signature.