Access restriction for child tables - property button missing

I want to restrict access to certain fields based on the role of the person logged in. I am able to that for top level fields using the ‘Properties’ button.

But for a child table field, the ‘Properties’ button is missing.

I want people only of a certain role to be able to modify values of a child table. For the rest, it should be read-only.

How do I achieve that ?