Open Settings
Tap General
Tap Software Update
Tap Automatic Updates
Turn off Download iOS Updates
Turn off Install iOS Updates
Go to Settings
Tap App Store
Turn off App Updates if you want to stop app updates
Go to Settings
Tap Battery
Turn on Low Power Mode to help delay some background updates
Go to Settings
Tap Screen Time
Tap Content & Privacy Restrictions
Restrict changes if needed
Avoid connecting to Wi-Fi if you do not want updates to download
Delete any downloaded update from iPhone storage if already downloaded
Go to Settings
Tap General
Tap iPhone Storage
Find the iOS update file
Delete the update file
Keep enough storage free to control update behavior manually