If you click on the Facebook icon (left to your post) you can select from multiple post settings.
Save as Ad, this will save the post to Facebook as unpublished (also known as a dark post), it can be used for ads and it will be visible in Facebook Ads Manager. After performing this you have the following options to find it in Ads Managers.
Once you’ve saved them as a draft, go to Ads Manager, click on the top left corner on business tools (right below the “home” icon), and select Page Posts.
Click on it and you’ll find your post in “Ad Posts”. Select it, click on Actions at the top of the page and hit create ads:
Save your first Ad to Facebook 👇