Menu button for very old apps in Android 7

I have Lenovo TAB4 10 Plus tablet with Android 7.1.1 and I'm unable to change settings for some very old application because of missing menu button for them. In Android 5 there was *floating menu button (with 3 vertical dots)*, and there was also a possibility (in general options of OS) to change the behavior of the task button - *long press on it opened the application menu*. But now there is no floating menu, no possibility to change the behavior of task button (nor home button, nor back button). I tried the long press / double tap on all three buttons (home, back, task) but without success. Is there some way to display menu for such old applications? **Edit:** It's not a duplicate of the question How does one use apps that place a menu on the system bar when the buttons are not in the screen? , because I tried using both answers in the question but without a success - neither recommended procedures, nor the recommended application Menu Button helped me. The last one created the (new) menu button, but it opened *Android settings*, not the active application's menu.