Hey there, Milos,
Thanks for visiting the Apple Support Communities. We understand that you see an app listed under usage of your iPhone that is titled as "Recently Deleted Apps", and you have some overall privacy concerns. We'd be happy to help!
The Recently Deleted Apps you're seeing is likely residual information from an app (or apps) that has been deleted recently. Your phone logs your battery usage per app over the last 24 hours, and the last 10 days. If the app(s) was deleted within the last 10 days, some information may still be visible under Settings > Battery.
The good news is that apps can only be installed onto your phone by someone who physically has your phone in their hands.
We appreciate wanting to make sure your device is secure from top to bottom, and encourage you to review the following Apple Support articles to get more information on Apple's security for their devices and operating systems, and tips to using the security features built into iOS:
About privacy information on the App Store and the choices you have to control your data - Apple Support
Use the built-in security and privacy protections of iPhone - Apple Support
If an app asks to track your activity - Apple Support
Legal - Data & Privacy - Apple
About privacy and Location Services in iOS and iPadOS - Apple Support
Use private Wi-Fi addresses on iPhone, iPad, iPod touch, and Apple Watch - Apple Support
Have a good day!