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.
This might help you: Xperia/AOSP NavBar Buttons. A pre requirement is root access and Xposed. I found only this alternative way for your device for the menu bar, but it might not worth.

Or try Custom Navigation Bar.