Apple has made the beta version of macOS 10.13 High Sierra publicly available a few weeks ago. With a new Operating System, there can always be unforeseeable issues. GRAPHISOFT is actively testing the new macOS version to identify all of these potential problems. We have created a Help Center article that provides always up-to-date information about compatibility with macOS 10.13. We have also linked all already known issues into it: https://helpcenter.graphisoft.com/?p=74160
GRAPHISOFT plans to maintain compatibility with this new OS for ARCHICAD 20 and 21. Our compatibility Updates are planned to be released once macOS 10.13 is officially released, as it is largely due to change in the Beta phase. Therefore our compatibility updates can be expected towards the end of the year.
Until further notice we strongly advise against installing macOS 10.13 High Sierra on production machines.