There is generally no reason to force close an App that is operating normally. Due to the design of iOS/iPadOS, Apps consume virtually no system resources when they are dormant. Force closing and relaunching an App is also not power efficient; relaunching an App requires the App to be fully re-initialised, whereas resuming from a saved state requires significantly less power.
If you need to force-close an App, check that you are using the correct method...
Swipe upwards from the bottom edge to the centre of the screen - and pause briefly before lifting your finger from the screen. This will open the App switcher page - that will show a thumbnail image of each of your open (but not necessarily running) Apps. To force-close an App, swipe the corresponding thumbnail off the top of the screen.