Once again: fresh installation of LXQT. That which comes with it by default, that is.
Learn to read carefully.
What makes you choose to overlook it? It must not be the first time for you to say one thing and do the other.
Fresh and latest version of LXQT.
Alt+Tab doesn't work at all. Is it how it's supposed to be? On every other Linux DM on Earth it will work properly.
I've done a search and found only 1 or 2 results which proposed a tangled solution.