Background Redresh

Try a forced restart.

• Press and quickly release the volume up button

• Press and quickly release the volume down button

• Press and hold the side button.

• When the Apple logo appears, release the button.

Force restart iPhone - Apple Support (IN)

You can turn it off in two places

a) settings, general, background app refresh.

that's where you can turn it off as a whole...now that said, even with that turned off new apps can still install with it on, so you have to go into the general settings, turn background refresh ON, then you can turn it off in the app list below AND also turn it off in each app's main settings (the settings for each app in the settings tab)

they make you work for it :)

then once you have everything off you want off, you can turn it back off in the main settings if you wish.