Current stacking alternatives do not reflect reality. The use case of this functionality does not take into consideration that you often need to stack the first and the second item on top and the middle behind (For example, a carousel gallery with right/left arrows that half overlap the image. This problem makes the stacking function add problems to Figma, not increase functionality. I hope you will solve this issue asap,
You could achieve that with absolute positioning for the arrows, they will be sorted to the front.