I think I found a bug with Field Rules when Previewing a Form.  Specifically, it appears the field rules to enable/disable a date/time field don't appear to be working when I Preview the form.  They do work as expected when I run the form in Test Mode, so I think this is just a bug with the Preview functionality.

I'm on Version 12.0.2503.10378 and using the Layout Designer.

I have a Field Rule that is enabling three fields (two number fields and one date/time field).

When I preview the form, I can see all three fields are disabled when I have not selected the task from the drop-down.  But when I do select a task, the number fields work as expected but the date/time field does not.

Here's my Field Rules:

And here is how the fields look in the Preview:

When no task is selected, they are all disabled:

When I select the task where they should all be enabled, they are enabled:

But when I select a different task where they should not be enabled, only the two number fields are disabled, while the date/time field remains editable.

I tested both Enable and Disable options and both Steps and Stages and saw the same behavior.