I also built a whiteboard out of glass, although my approach was a bit different. I also made 3d printed spacers with a screw through, but I also support the whiteboard itself on thin wood strips that rest on the skirting below.
I was a bit worried about the whole weight of my heavy glass whiteboard depending only on those spacers.
Something like that should be made from tempered glass, not ordinary glass. Ordinary glass breaks into sharp pieces if broken, and if those shards land on carpet it’s incredibly hard to remove them all. A glass splinter to the foot is a serious lurking problem.
The product is SHAPE brand Sheet Glass, and the product description says it is "for use in picture frames, replacement window panes, painting, and other crafts and household projects", which I figured was enough of an endorsement for this use case. Not safety glass, but maybe I'll swap it out if the whiteboard ends up getting a lot of use and I keep it around longer term. This is essentially a prototype, so definitely open to changing things as time goes on.