Update
You can only update using Wi-Fi on iPhone 11 but the average person doesn’t have Wi-Fi in their house so why do you keep changing the iOS
iPhone 11, iOS 15
That's not an Apple choice. It's a request that comes for cellular carriers to avoid clogging Internet.
Updates are always important because contain bug fixes, new features, and very often security patches.
To perform an update procedure wirelessly, you need to connect your device to a reliable and fast Wifi Network with internet access (no cellular data, unless you use a 5G network, no personal hotspot on your device, no VPN connections, no low power mode are admitted). AND I suggest that you keep the device plugged into power during the whole update process.
If you don't have a wifi network with Internet access, "borrow" one from your friends/neighbors, or ask for help at an Apple Store or Authorized Service Provider or Authorized Reseller.
Do not forget to create a full backup of your device, before any updates.
Regards
Giulio