Change which sections come up automatically on actor's page

No. It's automated based on the number of credits. Remember, the pages are set up for users to be able to easily locate information, not to advertise what you choose. It's not really a resume (though you can add one via IMDbPro).

Of note, the reason there are more credits as calculated by the system, as opposed to the shown number of credits is that the system now sees each episode as an individual title. So you really have 65 writing credits. Your acting credits would need to exceed those to change the order displayed.

As a separate but related issue, perhaps in this case it may seem odd that
the first (Writer) credits section is the only section that is opened by default.

FWIW, to the right of the "Filmography" heading, there is a small
clickable option to "Show All" credits.  Click it, and all of the
credit sections will open (although they will remain in the same order).

Personally, from a user's perspective, I'd like to have an option
(in the Site Preferences settings) to "Show All" credits by default.