What is Rh used for that is so specialised that it cannot be substituted by another PGE? It's a bit of a stretch to suggest that Mg and Mn are at all critical

What is Rh used for that is so specialised that it cannot be substituted by another PGE? It's a bit of a stretch to suggest that Mg and Mn are at all critical since they are major rock-forming elements without geographically restricted supply. Similarly, Sr is sufficiently abundant that we need not worry about running out, only the cost of extraction/recycling old CRTs.