To open two apps simultaneously on a Samsung device, use the "Split screen" or "Multi-window" feature. This allows you to view and interact with two apps on the screen at the same time.
Here's how to use split screen:
Open one of the apps: you want to use in split screen.
Swipe up from the bottom: of the screen and hold until you see the multitasking screen.
Tap the icon of the app: you just opened.
Tap "Open in split screen view" .
Choose the second app: you want to open in the other half of the screen.
You can now use both apps in split screen mode. You can also resize the two windows to your preference. To exit split screen, swipe up from the bottom to go to the home screen
Press the keep app open button in the recent apps menu. If your phone only allows you to have 1 app selected at a time, not much you can do. You could set an apps battery settings to unrestricted.
Just note trying to keep an app running all the time is going to have a noticeable battery impact