If you are already on a version of macOS, you can use the Terminal to fetch the installer:
Open and create a bootable USB drive with at least 8GB of storage. download+macos+high+sierra+10136+exclusive
sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume Alternative Tool : If Terminal feels daunting, tools like Disk Drill offer a visual "Create Boot Drive" feature. Quick Checklist Before Installing If you are already on a version of
sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/[Your USB Drive Name] or Catalyst frameworks.
You aren't looking for the latest features; you are looking for
High Sierra is objectively snappier on older SATA SSDs. The kernel is lighter without the weight of SwiftUI, Sidecar, or Catalyst frameworks.