Just like in the UK, if you sell property in France for more than you paid for it there is tax to pay. If the property is your main home then there is a 100% exemption (so you’ll have no French Capital Gains Tax to pay). If the property is a second home then things get more complicated.
I’ve been collecting some articles on the subject from the web. A good place to start would be the French Notaires website.
More from the French government here. Dealing with the specific case of what happens when there is a delay in selling what was a principal residence.
and some Brexit related comment here