Thanks for your feedback.
We have modified “step forward/back 60s” shortcuts from combined keys (Alt + left arrow / Alt + right arrow) to “arrow up/down”, because in most of the conditions, you can use mutiple ways to control the volume, e.g. Mousewheel, Function keys, Touchpad/Touchbar. However, step forward/back is a more frequently used feature with few ways to control, so we change it back to the keybind that we set in the legacy version.
And yes, we will think about allowing users to adjust volume higher than 100%.