I strongly oppose any form of ethnic separatism in the US. I strongly support integration. So, to your question of when will we return Brooklyn to the Lenape? The answer is never... but they are free to join America and become full citizens like everybody else.

People confuse land with nations. Prior to Europeans arriving in North America, the land we now refer to as the United States, was occupied by the previous conquerors. Those conquerors overran and absorbed the previous people living in North America much as the Europeans did thousands of years later. Nothing new under the sun.

https://www.livescience.com/archaeology/the-1st-americans-were-not-who-we-thought-they-were

Unlike other nations where ethnicity is often used to determine citizenship, from the beginning, the US opted to follow a different path. Some anthropologists argue that we had no choice. The country needed far more people than it had to realize its full potential... unlike other countries and you apparently, our forefathers were not stuck up with where you were from or what genes you had.