How to prevent iOS from closing (or suspending?) an app that is not active?

I’m using iOS 26.2.

I have an app that I use to do language flashcard reviews on. I used to start a review session, do some reviews, then leave it open in the background, and continue later.

Recently, I noticed that the app was closed (or suspended) by iOS, so when I want to return to the session, the app instead starts up from scratch. This is a problem because I’m losing some unsaved review progress.

Can I stop apps from being closed like this, or at least increase the time until they’re closed?