I provided a link in the post that directly addresses this issue. I believe your question is sincere, but I have no interest in repeating myself or trying to convert you. Maybe give the article a read. It lays out the libertarian position on open borders and addresses criticisms raised by some.
Here it is again:
https://www.libertarianism.org/columns/libertarian-argument-open-borders
Here are a couple more resources. If, after you've read them, you still have genuine questions about foundational libertarian principles, I'll be more inclined to answer them.