You can switch between App Windows, or individually force-close Apps, from the App Switcher. There isn’t a gesture or key-combination that will simultaneously close all open Apps.
To expose the App Switcher, it is necessary to swipe upwards with your finger from below the active portion of the screen, to the middle of the screen - and pause briefly - before lifting your finger. Once visible, open Apps can then be closed by swiping the corresponding App thumbnail off the top of the screen.
Alternatively, the App Switcher can be summoned by a double-click of the Home button on iPads so equipped.
You need to be aware that forcing-closed an App is generally unnecessary. Force-closing and relaunching an App uses considerably more power than just resuming an inactive App when needed.
Some understanding of how memory management works within iOS/iPadOS might be useful to you. To be clear, this is not intended to be an in-depth explanation, but will hopefully capture the essentials in basic terms...:
Your iPad/iPhone will always attempt to use most of its available RAM - unused RAM in this low power/high performance system architecture is essentially wasted resource.
iOS/iPadOS Apps are generally in one of four states - the first three are the most relevant.
- The App is “Active” - it is running running in the foreground. When you switch tasks, the App will continue to run in active state for some minutes before its resources are released and is placed into an Inactive state.
- The App is “Inactive” but remains loaded in [fast] RAM. In this state, the App can be instantly restored to an Active state - but is not consuming CPU or other resources whilst in the inactive state.
- The App is “Inactive” and unloaded. In this state, the App has been completely offloaded* (releasing RAM for use by other processes) but its running state has been saved to [slow] flash memory. Returning to an App in this state will cause the App’s saved state to be reloaded from flash memory into Active RAM - without the need to re-initialise the App.
- The App has been closed. All running data has been expelled - there is no “saved” state; relaunch will reload and re-initialise the App from scratch.
Memory management is generally a juggling act - and for the most part, you should allow the OS to manage its memory space. Re-initialising an App is the slowest and most power hungry method of launching an App. Inactive Apps do consume some system resources, but by design, the required system resources to maintain this state are insignificant.
Force-closing an App releases all resources. Whilst the mechanism exists to do so (and in rare circumstances manual intervention to terminate an App may be necessary), a force close reduces system performance.
(*) “Offloaded” in this context refers to active system resources. This differs from App-offloading to provide additional temporary local storage space.
If you are new to iPad and iPadOS, the iPad User Guide is a rich source of frequently overlooked information. The Guide is available both online using a web browser (such as Safari), or as an Apple Books download:
iPad User Guide - Apple Support
https://books.apple.com/book/id1567104892
The Tips App, installed by default on all new models of iPad, provides a brief introduction - and leads you to the User Guide. In case you missed it, here is a link to the Tips App:
https://apps.apple.com/app/tips/id1069509450
Apple also has a huge YouTube Channel - containing videos and feature guidance:
https://www.youtube.com/user/Apple