Why this update takes to much time ? Still unable to update iso 13.6.1 . It’s show continuously Estimating time remaining.

You can't update without being connected to a reliable and fast wifi network.

That's mandatory to perform the update procedure, and you cannot use a personal hotspot. If you don't have a wifi network, "borrow" one from your friends, or go to a public place with wifi/internet capabilities.

Regards

Giulio

Connect the iPhone to a WiFi network and try again.

Connecting to a HotSpot will not work.

Seeing your screenshot, you are using your personal hotspot, not a wifi network.

Regards

Giulio

Connect the iPhone to a WiFi network.

The screenshot shows otherwise.