Looks like this is working if the Action “Runtime” is set to “Node 18 (Recommended)”, but will not work with earlier runtimes, like “Node 18 (Beta)”.
My Action was on “Node 18 (Beta)”, and I clicked the “Upgrade” button, which changed it to “Node 18 (Not Recommended)”. So then I had to manually delete the Action, and recreate it with “Node 18 (Recommended)”, and now the “event.user.XXX” references are working.