It's not really related to the Android version, but rather the manufacturer. It's up to the manufacturer to implement these kinds of features, and some decide not to.
Since you have a phone with Oreo, there's a possibility the card can be formatted as Internal Storage (which is called Adoptable Storage). This makes the phone regard the card as part of its own internal storage, which can therefore increase not only the storage capacity but also the space to install apps. However, we generally recommend against this, since SD cards are generally less reliable, and if/when they crash or become corrupt, that can cause some significant system instability.
You can tell if your phone supports Adoptable Storage by seeing if it asks you if you want to format a card as Internal Storage or Portable Storage.