Shadergraph Matrix cannot be exposed - Unity Bug?

When using Shadergraph (im using a PBR Graph on URP for WebGL), there is a possibility to use a 4x4 Matrix as property. However, I cannot set the matrix since it is not exposed. There are to ways to create a exposed property, and none of them work:

1) Adding it with the "+" sign in the property panel, I cannot tick the "exposed" tickbox, its grayed out: 

2) Create a new matrix input node, right click -> convert to -> property. This works and also gets shown as exposed in the GUI. Although the "exposed" box is ticked (and cannot be unticked).

In both cases, the property is NOT exposed and the matrix cannot be set via script. The generated Code also does not have the matrix property. Is this a unity bug or is there a workaround? Same procedure works fine with a vector1. I cannot set all values separately with a vector1 or similar due to the WebGL uniform limit.