iPhone X: lots of problems

Hi.

Since a couple of months I'm experimenting lots of problems with my iPhone X.

• requesting an App d/l from App Store take 3 to 8 minutes before asking for confirmation to download
• after reinstalling iOS (either latest relases of 13.x.x, 14.0, 14.0.1, 14.1) there is no way to configure it. After connecting to Apple's servers it starts from scratch. And is a loop.
• I intalled iOS also in DFU mode. No way to configure it as above
• managing any operation that requires connection to Apple's servers takes a long time (see first point). I don't believe it's a matter of Apple ID as form Ipad and MBPro everything is OK.
• I went to the nearest Applestore and they told me to call the Apple support. I called the Apple support and they remotely verified the HW is OK. They told me I would be called back by more expert technichan. Looks like that the problem is in iOS but related specifically to the X model.
• everything else is working perfectly. Downloaded apps work perfectly. I'ts only when a connection with the Apple's servers that everything terribly slow.

Hoping in iOS 14.1.1. or 14.2, any suggestion is appreciated.

Thanks

Simon

(iPhone X 256GB - iOS 14.1)