Yes, you can. In the "Ads" section, navigate to the "Existing posts":
There, you’ll see a list of available posts for Facebook and Instagram:
You can:
Preview each ad
Check engagement metrics
Filter by type (available for promotion, ad post, scheduled, or published)
You can choose either Facebook or Instagram posts - but not both in the same campaign.
Note: For Instagram, only image and carousel posts can be used as existing posts for ads. Video posts cannot be used, as they are not processed via the Meta API.