External Keyboard Malfunction after Cleaning

I’ve been using a Microsoft Natural Ergonomic keyboard 4000 (USB) with my Macbook Pros for years without a problem. I had a cleaning crew over this morning & right after my office was cleaned, it began malfunctioning. They must have accidentally engaged some kind of keyboard shortcut when cleaning my keyboard.

• When I hit “ENTER”, an “x” is typed & vice-versa, as if I was pressing them together. I can't even hit enter when logging in, because it adds an "x" & causes the password to be incorrect.

• The “Select keyboard” dialog (attached screenshot) keeps randomly reverting to “Unifying Device” or “USB Receiver” rather than the correct keyboard.

Another aspect complicating things - it starts & stops for no apparent reason. It’ll suddenly begin working normally, but then I’ll hit “x” & “ENTER” a few times & it’ll return. When it does go away for a few minutes, other keys begin malfunctioning too: the tilde renders this: ± and the slash adds a 3 after it: /3.

I've tried the following & a few more tips I found online, to no avail:

• Reset the SMC
• Tried British keyboard layouts
• turned off the toggle input sources shortcut
• Disconnected all peripherals
• Turned off “Key Repeat” function

 I’ve seen a lot of other folks referring to similar problems after upgrading to Big Sur (I'm on 11.6.1), but this has to be something that was triggered when the keyboard was cleaned…The timing can’t be a coincidence.

Any advice appreciated – this is really driving me crazy.

Thanks.