Hi Isleofgough,

re:
> Unfortunately, this beta version will not open in OSX 15

I set up macOS 15/"Sequoia" over here and the v5 beta is working fine for me after following the install readme instructions.

For MoI v4, it used to be enough to right click on the app and choose "Open" on the pop up menu for the first time running it. But with Sequoia that won't work anymore. You instead need to go to System Settings > Privacy & Security and there will be an option there where you can allow it to run.
Some more info on this here:
https://www.idownloadblog.com/2024/08/07/apple-macos-sequoia-gatekeeper-change-install-unsigned-apps-mac/

- Michael