My power button is not working

@muhammadal69023 you need to check the mechanical part of the power switch to make sure that it actually closes the contact. If that looks like it is working, then replace the power button flex. Since iFixit does not have a guide for this yet, use something like this for that. The power button flex also has the fingerprint sensor on it. It is readily available at many online stores.

If that should not resolve it, you will need to check your mainboard for a missing/failed component. Start with your power flex first.

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.