I click on software update and I tried updating my iPhone X but it only says Estimating time remaining? I want to know if it’s stuck or I’m already downloading update

Check all of these carefully:- 

you are on a good Wi-Fi, (from 15.4 iPhone 7 up, you may be offered cellular update)  and  that the router is connected to the internet. 

Plenty of spare storage – 6GB at least. 

Low power mode turned off and on charge with more than 20%, or off charge with more than 50%

Check you have no Beta profile installed. (Check Settings, General, VPN & Device Management) 

no VPN installed (Check Settings, General, VPN & Device Management)