You need to output those fields in the template, which would require either:
a. A custom PHP template for your posts
OR
b. the easier method is to use GP Hooks to insert your fields into the template:
https://docs.generatepress.com/article/hooks-element-overview/
ACF provides documentation on the code it requires to display its fields here:
https://www.advancedcustomfields.com/resources/the_field/
We can help with the hook method … Let us know if you need any help with that.