The can't tab out cause of DirectX 11 is a critical issue and needs to be fixed. Was this issue not reported when DirectX 11 was optional for the game a few months back?
https://forums.ea.com/discussions/the-sims-4-technical-issues-pc-en/alttab-not-working/4946821
and yet it was decided to add DirectX 11 in the latest patch despite knowing this would cause a problem and remove a key feature from the game. Reverting to DirectX 9 is only a band aid fix, and is unfair for players not to experience the full benefits and improvements of DirectX 11.
The removal of this pivotal function will be a huge dealbreaker for most players and will undoubtedly turn them away from playing this game. Surely the game developers have the capabilities to fix this? Other gaming titles have the function to tab out with DirectX 11 , so why not Sims 4? The game development community has already discussed how it is done.
https://gamedev.stackexchange.com/questions/169673/what-actions-should-i-perform-in-directx-11-to-correctly-process-alttab