Fieldset not showing in new tab

Hi support

1. I have a problem showing a fieldset in a new tab created in Details page.
In the Event cpt I created a new tab where I put some custom fields and a fieldset. New tab and fields are displayed correctly but the fieldset is not visible in the new tab of Details page, it shows only in the Add Listing page.

My specific fieldset setting are:
Is active = yes
Show on listing page = no
Show in More Info tab = no
Show as a tab on Detail page = no

I tried all combinations between these options but fieldset never appears in the new tab (it only appears as a new tab if I set to yes “Show in More Info tab” and “Show as a tab on Detail page”).

Am I wrong or is there a problem?

2. What is the best way to style the fieldset once it will be visible on the detail page?

Thank you