How do I replicate this behaviour in cylc 8? The help message implies I should create a ~/.cylc/global.cylc file to control this, but I only need this on certain suites.
You should use the archer2-nvme platform which will set up the symlinks for you. Make sure any tasks in your suite that run on Archer2 use either archer2-nvme or archer2-nvme-bg as the first task that runs is the one that sets up the symlinks.