Summary Block doesn’t support Portfolio Page, however you can use Blog Page, then use Source URL feature to link to Portfolio Page in Summary Block. Follow these steps.
#1. First, create a Blog Page with some blog posts
#2. Hover on all blog posts > Click 3 dots icon > Settings
#3. Enter the Portfolio item URL here then enable the option “Link Post Title to Source URL”
Here is example with my portfolio page (you can also enter full URL)
#4. Edit page where you will use Summary Block > Add a Summary Block > Choose Blog Page
