Today, all of the latest generation consoles are able to keep games on standby when you exit to menu. Xbox Series X will be able to keep multiple games on standby so that switching between games will be even easier.
The console can run games with 4K resolution and 60 frames per second or go as high as 120fps and 8k resolution. Gamespot's interview with Microsoft revealed that the console also will be capable of running games simultaneously.
If you want to switch between Mortal Kombat and FIFA for example, you will be able to do it. You will be able to do it and its waiting time will be less than a second.
Partner Director of Program Management for Team Xbox, Jason Ronald says, "Many players choose to play multiple games at the same time, being able to instantly jump right back where I was, those are things that we can do with the platform level to make the gaming experience better."
The team seems to be focused on developing an immersive gaming experience without any disturbances. Technically, the console is capable of doing this. The question is, will Microsoft be able to manage to create a good enough software to support this? Xbox Series X will show it to us.