There is no way to force close all your apps. It's not typically a problem however it should be avoided, especially the foreground app. "Forcing" software to do anything outside its own programming isn't typically wise due to variables the developer can't account for.
Force closing an app in iOS is like Force Quit in MacOS or End Task from Task Manager in Windows 10. A healthy app cycle includes the opportunity to tidy up, save data, release its resources and end the app process. Apple says it should only be used for unresponsive apps (like MacOS and Windows force quit).
In iOS an app moved to the background is given a few seconds to perform those shut down steps to prepare itself in the event resources are needed and iOS (or the user) terminates it operation. iOS will send out low memory warnings that give apps the ability to release memory using assets.
Allowing iOS to handle it is typically better for battery life because iOS can keep the entire app or portions of the app ready to reopen without the CPU needing to start from scratch reading data from NAND.
There are a lot of variables here when it comes to the app actually doing something in the background if it has access to API's that allow background operation but thats a different topic.
Regardless if this literally triggers your OCD there isn't going to be much you can do about it. You gotta do what you gotta do but unfortunately there isn't a 'close all'.