Settings > Battery > turn off Battery Saver and Adaptive Battery

Settings > Battery > Battery Optimization > click on 3 dots in top right corner > click on Advanced optimization and turn it off

Lock the app on the Recents screen (the multitasking screen)

To turn off background app notifications go to Settings > Notifications > click on 3 dots in top right corner > show System Apps > Android System > untick Apps Running in Background

On some OnePlus devices there is also a feature called App Auto-Launch which essentially prevents apps from working in the background. Please disable it for Safe Lagoon