The application switcher is my preferred way of launching apps. I added about 10 frequently used apps to the list. This worked fine for years. Inactive apps were greyed and clicking on them would launch them. As of last week the application switcher only shows the apps that are already launched, non of the others (so I have to revert launching them “old style”).
Click and Hold on any icon in the switcher and a menu will appear showing you the display options and the keys to toggle them. You presumably inadvertently pressed one of the keys (a) and toggled the display of the Always Included apps off.