Strange Icon on Taskbar Windows 10

Solution 1:

That's a toggle indicator for what your function keys do. Try doing Fn-Esc and you will see it toggle.

In one state (lock symbol but without the little round symbol in upper right) you get only the F1 through F12 functionality unless you press Fn first - in which case you then get the other marked multimedia function.

In the other state (with the lock symbol having little round symbol upper right), you get the multimedia key functionality without pressing Fn but then have to press Fn to get the F1 through F12 functions.

If you disable the item named "QuickSet" in startup, you'll find the Mystery Icon gone.

Source