Running Windows 11 Pro, version 21H2, OS build 22000.613

3 monitors, in case it matters.

The first version of Start 11 I tried was version 1.2, since I don't use the Windows start menu at all, so was only interested in having the taskbar updated.  So I don't know if earlier versions were also effected, but I found one thread that might be similar.

Normally when I Alt-Tab to Microsoft Excel (Microsoft 365 MSO, version 2203, 64-bit version) the current spreadsheet gets focus, so using the arrow keys moves the current cell in the spreadsheet.

With Start 11 installed when I Alt-Tab into Excel the Ribbon bar has focus, as if I was in Excel and pressed and released just the Alt key, and keyboard actions try to change tabs in the ribbon bar, etc.  I had to press Escape to get back into the spreadsheet.  This happened well over 95% of the time, it felt close to 100% of the time, and drove me up the wall.

I was normally moving from an active program on the central monitor to Excel on the right hand monitor, but I doubt monitor position had an effect.

The problem did also show up occasionally with other programs, but it was much less obvious, but I did notice it with "EditPad Pro 8"

After a couple of days I put it together that it started happening after installing Start 11, so uninstalled it, and the problem disappeared even before the required reboot to finish uninstalling.

I have Object Desktop Manager, CursorFX and Groupy also installed, but no other Stardock software.

I do have "autohotkeys" installed, to manage keyboard shortcuts, along with "Microsoft PowerToys", but PowerToys only keys to a few keyboard shortcuts, only one of which includes Alt, which is Alt-Space for PowerToys Run - which is why I never use the start menu.