Change setting for apps in the background?

As you can see in the picture, the apps in the background, on my Huawei Mate 20 Pro, can't be viewed. Normally, I would have to see the called app, but it's just a gray area there. I would not remember if I had changed anything.

Would you like a solution?

Ever tried to restart the smartphone? Sometimes the simple tips help, especially when it has not been turned off for a long time.