I love Mouse Without Borders, but holy cow do I not understand how it doesn’t have a function to remove old machines from its settings. It seems like a ridiculous oversight. At any rate, I figured out how to do it. This is as of Powertoys v0.83.0. As per usual, you’re poking under the hood, so be forewarned.

In Windows 10/11, the settings for MWB is stored in a .json file found in C:\Users\YOURUSER\AppData\Local\Microsoft\PowerToys\MouseWithoutBorders. AppData is a hidden dir, so you’ll either have to enable seeing hidden dirs or path to it directly. Open the file in a text editor – I use Notepad++ – and head down to around line 45. There you’ll find MachineMatrixString. Delete the machine names you want to remove from MWB and replace them with empty quotes. Head to the next section, MachinePool, and again remove the machine name and the corresponding value following it, separated by a colon (if it’s a long-gone machine from your network, that value may be NONE) and replace it with a colon. You’re going from something that looks like this:

To something that looks like this:

Note that the before settings depict 3 machines and 1 empty slot and the after settings depict 2 machines and 2 empty slots. Mouse Without Borders has 4 slots for machines. If you just delete the machine you want removed and don’t repopulate with empty values, the MWB UI in PowerToys will lock up.

In my experience you can now save this file and don’t even have to restart PowerToys or MWB. Open the UI and click into MWB or, if you were already in MWB settings, click out and back in, and your machine settings should be automatically updated.