In my case, it was working after installing VcXsrv (didn’t use VSCode, though) as I said in my last post of the thread I linked.
However, in more recent versions (of WSL, I suppose) the problem partially reappeared: the menus again show up in random locations, but at least I am able to click on them –with the cursor seen at a different place, but the menu items are highlighted and clicking works. By the way, VcXsrv is no longer needed; ROOT works the same (and the same visual issues) with or without the additional (apart from WSL itself) X server.
From what I have read online it seems to be something related to the GUI toolkit (Tk, I guess?), but that’s beyond my current understanding, so I just live with it and hope it continues to work 
I use linux most of the time, so fortunately I don’t face these issues too often. In any case, ROOT is moving to opening the canvas/browsers in web tabs or windows, so maybe this will not matter at some point; perhaps you can try that, you just may or may not need to install a browser inside WSL for this to work, if it doesn’t open on the browser you have on Windows –I have not done it on WSL, so I’m not sure.