Your system information
Further testing shows that you can regain focus when there are no other pop-up windows "between" the Steam Client main window and the "Move Install Folder" pop-up. The pop-up window also stays on top of other windows (such as a web browser) and is not in the Alt-tab menu.
Minimizing the steam client seems to give the move window its focus back.
The "Uninstalling " window seems to inhibit the same behavior.
Still not fixed on build 2020-02-11T19:27:00 (Manjaro x86_64 steam-manjaro-1.0.0.61-7, DE is Plasma 5 X11). To reiterate, the window appears to be keep-above, but behaves as though it's keep-behind; it cannot be focused with a click if there's another window over it (visually, behind it). Is it so hard to delegate window management to the window manager?
On a related note, is there a technical reason I can't open the context menu on ANY of Steam's window decorations? It's the easiest way to move windows to another desktop or set them to keep-above.
I assume this is now fixed since the move dialog has been remade.
Works fine for me now
Nope. Here's a video of me clicking where the dialog is and hitting the thing behind it. I forgot to show it, but the build date in About Steam is 2021-07-20—is there a newer version with a fix?
It is fixed in the beta build
Closing per the last handful of comments.
Nothing extracted yet.
Your system information
Please describe your issue in as much detail as possible:
Describe what you expected should happen and what did happen.
The Move Install Folder location prompt can lose permanently lose focus if you click anywhere off it. Though it does still render, the window appears to ignore events. Only work around is to go back through the process of moving a folder.
Didn't go through them all but couldn't find any other dialogs that do this.
Steps for reproducing this issue:
Repeat step 2 to regain focus.