Shortcut to move a track in the same track to get mixed

Hello, I would like to know if there is a shortcut to move a track to the track above, because I know that there is a Shortcut that says you can move a track, but up or down and what I want is to move a track to the same track so they are mixed together.

There is no default shortcut for that, but you can make a custom one.

See these two commands, they will mix and render selected tracks:

See this section of the manual on how to create a custom shortcut for either or both of those commands:
https://manual.audacityteam.org/man/keyboard_preferences.html#custom

Peter