Z-fighting when disable depth off.
I think if the translucent section of the selection box is slightly larger than MC default, the Z-fighting will not happen.So I suggest adding an option to adjust selection box size, so that users can adjust it to make best effects for their devices.

Hmm, I should've expended the selection box by a little bit, not sure if I removed that

there is still some Z-fighting for the latest release.

On the 1.15 version?

Yes, the one you uploaded recently, if you look at the vanilla outline very closely, it is slightly bigger than the block. The mod's outline is part of the block edges, which causes the z fighting