I think the main problem with this post is that you didn't explain how it's not working for you. You asked how do I share posts to Facebook news feed, I have tried for days. So in what way is it not working for you? Some more detail around this would've helped other users work out what you could be doing wrong and I see now the thread has become requests for your C3 file anyway.
Looks like Ashley's comments are implying that although possible to share to the news feed using IG according to SDK documentation, maybe it isn't possible in Construct 3 plugin and you can only share to the messenger part. OP you will have used this more than me, maybe you can explain what you tried and what is and is not being shared when you use the share part of the plugin.