As Aperture is no longer macOS compatible moving forward and I’m not yet ready to fully let go (still hanging-in for an Affinity solution) while still wanting to moved forward with macOS, I am looking to partition and install a bootable OS just for Aperture. I’m not intending on being online for this OS so OS security is not a concern.
I remember at some stage one of the OSes brook Onscreen Proofing or something related to the advanced printing profile (back in Mountain Lion days maybe or even Mavericks???) but also was it around Sierra days that some reported the OS upgrade making it snappier again.
So any thoughts on what was the best OS for Aperture 3.6 (as opposed to the best OS - we all know that was snow leopard ;o) that I should revert to?
I think it was soft proofing that you are referring to; I’m pretty sure it stopped working by Mojave, and maybe the one before…
If I remember correctly, the last update to Aperture (version 3.6) was to make it compatible with Yosemite ( with was macOS 10.10) it was followed by Mavericks, Sierra, High Sierra, Mojave and finally Catalina. So, it would be pretty safe to run Aperture on Yosemite, because with later OS some bugs may have appeared.