Any ideas? Yes.
If you are not using a child theme then create on and change to it.
Create an override template for buddypress where you want to add the gallery to be edited https://wproot.dev/blog/override-buddypress-template-files/
Use acf_form(), supply the correct post ID for the user "user_{$user_id}" and set 'form' => false and other settings as needed to show the groups/fields that you want to add https://www.advancedcustomfields.com/resources/acf_form/ In the override template place the call to acf_form() inside the existing buddypress form.
