Thank you Erel. It looks like I figured it out. At least I found one way to do it. You have to save the video to File.DirExternal, otherwise Instagram won't pick up the file in the "android.intent.extra.STREAM". Also, it requires "content://" instead of "file://" in the uri. I tried many times in every way possible with the FileProvider approach, and Instagram never recognized, or allowed the extra.STREAM info in.
This works:
Dim u As Uri
u.Parse("content://" & File.Combine(File.DirRootExternal, FileName))
intn.putExtra("android.intent.extra.STREAM", u)