I was having this issue with only an external keyboard and found out that somehow(probably my baby playing with my keyboard) the switch for macOS or Windows on the back of my keyboard had been switched. So alt and the windows key had been swapped. Windows tab does the 'new' weird version of alt tab that a lot of you are describing.
If the multitasking settings stuff didn't work for you(like it didn't for me) make sure your keyboard is made for windows and/or if it has a switch that it is in the right position.