It didn't sound like op wanted maximally dissimilar from what they've liked before, but instead maximally dissimilar from what they've listened to recently.
Either way, a preference for novelty can be measured. They also let you edit your Taste Profile it seems: https://support.spotify.com/us/article/your-taste-profile/
If your taste is exactly "maximally dissimilar to anything I have liked before," that's actually pretty easy to calculate from the embeddings as well.