Unknown app

I’m sure it was installed by someone who wants to remotely access my phone

No, it wasn't. "Astronomy" is one of the new wallpaper options released with iOS 16. It will show you live astronomical data.

Change the wallpaper on your iPhone - Apple Support

For future reference, when you want to find an app and can’t find it on your Home Screen, there are a few things you can do. One is to swipe down from the middle of the Home Screen (or tap the “ 🔎 Search” icon to access Spotlight Search. Then type the name of the app you are locking for. The other way is to view apps in the App Library which will show all apps. To access this, swipe all the way to the left. Hopes this helps.

Please see: Change the wallpaper on your iPhone - Apple Support

It has absolutely nothing to do with remote control of your device.