Hi Andrea, sorry for the delay…
If you paste your two URLs at https://dev.twitter.com/docs/cards/validation/validator (the Cards validator) you will see at the top level you don’t have any valid Twitter Cards markup but on an individual post, you do.
The fields you want to see are twitter:card and twitter:domain etc
I haven’t dug around in the Yoast SEO plugin but there may be a setting to have it applied at the root of your site instead of just on individual posts. Unfortunately we can’t easily support that on our forum here which covers all kinds of Cards issues, you’d need to check with the author.
The good news is - in general for individual posts, cards are correctly setup for your site and should appear in Details view when a link to your site is posted. Your domain is approved for summary cards. All looks good!