Version 121 has some new things under the hood, but for you to see, most important is a new setting under the Logo Menu: Mute Smoothing.
While muting, ArrangerKing automatically fades in and out your track, preventing clicks or pops that would interfere with your mix. The default smoothing is balanced, providing a clean fade, without destroying drum transients. If you need perfectly clean transients, or
softer transitions, you can change the smoothing length under “Mute Smoothing" in the menu settings.