A fairly simple change to consider. Or postpone until later. Or never...
When side panels (and headers) are closed or hidden, there is a little arrow that is used to show it again. I have always found the arrow to look a bit chintzy somehow, not matching the rest of the UI, and a bit small.
This patch changes it from what you see on the left, to what you see on the right:
On its narrow side, it intrudes into the working area no more than the current one. But is wider to make it easier to hit.
The two lines are meant to evoke the items are revealed, and their shape hopefully indicates what it does better than the current one.
It is carefully scaled. So it changes with user scale and also line width, without creating sub-pixel lines or gaps. or getting too narrow or wide.
I hope you like it. But will understand if you think the change unnecessary, especially at this time of release. It is also possible that the visual weight of this is more than we want, so it is worth testing in action.