Hi barberlives 123,
Thank you so much for replying me.
I tried all the steps and also bring to service center and got an answer that it's hardware failure.
So basicly, my properly working iphone X just dead because of updating to iOs 15. and there is no option that i have to throw it into trash bin.
That service center also told me that many same case happened andI can see a big cheating here at Apple to customers.
This is so unfair at all to all user. So beware everybody. Once your phone is old model, you have one option only, make it die by updating it and buy a new one!
So disappointed!