There are two options to achieve this result.:
You can use the Conditional Field section and set the condition based on the field itself.
Turn on the Hide field if empty toggle in the Standard Options. This will not affect the form when creating a record.
This feature makes the most sense when users are editing records (not creating new ones)
On the legacy site app.miniextensions.com
Follow these steps:
Go to your form's settings page
Select the field
Disable the option "Show this field when it's empty".