“This is known as “fee simple determinable” title and is part of common law.”
Try selling your land with deed restrictions that bar blacks from buying it.
This land being sold with restrictions that it may only be used as a park is deeply flawed. Any judge worth two bits would rule that restriction as a violation of common law property rights.
Correct, you cannot transfer with an illegal restriction. It is not an “absolute” right. Racial prejudice in land transactions has been illegal since 1866.
Dedicating land for use as a park is not illegal.
Being that parks exist, you can safely conclude that judges have supported such restrictions.