Why iPhone update keeps long like that ??

Because your carrier says you can’t. This has always been true, since the first iPhone.

If you have an iPhone 12, 13, 14 or 3rd generation SE you can update using a 5G cellular connection. Any other model you need a Wi-Fi connection, and not a personal hotspot, either.

richest288 wrote:

But now I’ve connected to WiFi now but still

Your included screenshot shows you are connected to a hotspot, not a Wifi network.