Software update but not Install my iPhone why

Thanks for posting the screenshot. You are unable to install the iOS update because you have Low Power Mode set to ON and your iPhone is charged less than 50% and you are not connected to a Wi-Fi Network.

1. Turn Low Power Mode OFF
2. Connect to a Wi-Fi Network
3. Charge your iPhone to more than 50% and leave it connected to electrical power during the update.

Axel F.

As your screenshot shows:

”This update requires at least 50% battery or to be connected to a power source.”

In addition to the advice posted by sberman above:

Connect to a WiFi network.

Turn off the Low Power Mode option.