Hello Alfredo,
Welcome to Microsoft Community.
Although in your description you claim to have tried various troubleshooting steps, we are not aware of what you have done. If you would like, can you share with us what troubleshooting steps you have tried? In particular, have you ever had your Surface Pen battery replaced?
Also, after you unpaired this Surface Pen with the Surface Pro 6, is it now the case that you can't pair it again? Or can you pair, but you can't click, drag, or write at all with the Surface Pen? Because we need to use this information to determine the problem is the source of the Surface Pen tip failure.
In the meantime, test to see if you can use your finger to click, drag, or write on the Surface Pro 6, which will help troubleshoot whether the problem stems from a screen malfunction.
Best Regards,
Mitchell | Microsoft Community Support Specialist