After switching apps with the
Cmd-Tab shortcut, when you return to the same app, the
Cmd key is still pressed and the shortcuts help window shown. You can then press
t, etc without having the
Cmd key pressed.
This is a known issue within iOS 13, and to get Apple to solve it we need your help. Please create a bug report within Feedback Assistant. We suggest that you use a similar title to ours: "Cmd key stuck while switching between apps with Cmd-Tab".