Startup Idea: Software Solution for Downgrading Mac OS and High Sierra with Security Support

Startup idea to develop a software solution that allows users to downgrade from a later version of Mac OS to an older one like High Sierra and Mountain Lion without compromising their internet security support. The software should be able to encapsulate older software for compatibility with the latest OS versions.

I am a freelance audio engineer on a pretty tight budget. I am currently using a 2011 MacBook Pro with upgraded RAM and SSHD. My web browsers had been bothering me to update to the latest OS (High Sierra) in order to ensure my security was being supported.

However, since the update to High Sierra, my Pro Tools DAW is no longer supported. While it will still open and playback, it is very buggy. The drop-down windows are all grayed-out and the track titles are no longer locked to their respective tracks.

I've tried with very little success to find a cure. Updating to the most recent Pro Tools release would be very costly to me, and wiping my SSHD and reinstalling an older OS would mean compromising my security.

I'm thinking of something similar to Wine, which encapsulates Windows software to use on Mac OSX, except bottling older software to use with later OS versions that they are not compatible with. Or perhaps just an easier way to downgrade Mac OS with updated security support. I've tried to find OS downgrading options on Google, but all solutions would require me to wipe my SSHD and compromise my internet security support.

"Downgrade High Sierra to Mountain Lion"

Right now I just cope with old buggy software, or abstain from using it at all.