Greetings Ksalandy,
As outlined in the error message showing in the screenshot you provided, you'll need to turn off Low Power Mode to enable Background App Refresh.
Low Power Mode reduces or affects these features:
5G (except for video streaming) on iPhone 12 models
Auto-Lock (defaults to 30 seconds)
Display brightness
Display refresh rate (limited up to 60 Hz) on iPhone and iPad models with ProMotion display
Some visual effects
iCloud Photos (temporarily paused)
Automatic downloads
Email fetch
Background app refresh
Use Low Power Mode to save battery life on your iPhone or iPad
Take care.