In 2021, I started a sole proprietorship and registered with the RCS. Several years ago, my parents gave me the bare ownership of a property. Can I include it in the declaration of unseizability?

Yes. Reminder: In the context of their professional activity, a sole proprietor risks their personal assets if the business incurs debts. As an exception, the law provides a mechanism to protect the primary residence by making it automatically unseizable (Article L526-1, paragraph 1 of the Commercial Code).
You can also declare "your rights on any land, built or unbuilt, not used for professional purposes" as unseizable (Article L526-1, paragraph 2 of the Commercial Code).
 

Good to know: Law No. 2022-172 of February 14, 2022, offers even more protection. Since May 15, 2022, entrepreneurs automatically have a professional estate separate from their personal estate, protecting themselves and their families from the risks inherent in their activity.