High Sierra on Mac Mini 2018

Instead of downgrading have you considered using a VM manager, like Parallels or VMware, to run High Sierra in a VM for these apps?

You can run modern Mac operating systems in virtualization - I'd recommend Parallels Desktop. You can download for a 14 day test drive and see if your music production software will run okay in virtualization. Frankly I'm a bit skeptical but I've been surprised in the past. But there's no way I'd trust High Sierra on a 2018 Mac mini for mission critical work. There are too many ways that can go wrong.

Hi, James Arter1 !

I must apologize because I am not seeing the need to run virtualization software, nor the need to install a previous version of the macOS to the Mac Mini. I would obtain an external hard drive - regular or SSD - and install High Sierra (plus whatever program(s) you need) on that drive. Then when you need High Sierra, simply boot the Mac Mini to the external drive.

I hope this helps, and good luck !

The point is that the 2018 Mac mini did not exist when High Sierra Was the current OS. That means there’s a chance that drivers will be missing or other issues could exist that would make the computer anything from unstable to unbootable. Is it possible the 2018 mini can run High Sierra? Well it wouldn’t be the first time a new Mac could run an older OS. But I wouldn’t trust it for mission critical work.

If it can't boot High Sierra, putting it on an external drive will not be a solution.