Dosdude said that they are unlikely to work on non-metal systems. It's one of the reasons I reinstalled High Sierra. You can downgrade by downloading a copy of macOS from the App Store and creating a bootable drive, then reinstall. You will need to back up as it will wipe the drive.
Why not just regress back to Mojave instead? None of the metallization of the standard macOS bundled applications has occurred there and you will be able to use the Safari 13 betas to access the browser improvements.