My question is, how can random genetic mutations be the cause of evolution if genes are not the determining cause of traits?
To be precise, genes are not the
sole determining cause of traits.
I don't see what this has to do with "how random genetic mutations be can the cause of evolution". Evolution is, by definition, about heritable changes to the genes. Such as are caused by random mutation.
'[G]enes' do not 'cause' traits
Yes they do.
For example, the cause of my having blue eyes is that I have two copies of the blue allele for eye color. Reflection on this fact should answer your question:
[H]ow can random genetic mutation be said to be the responsible mechanism for the origins of biological novelty?
It is obvious, is it not, that when the allele for blue eyes was produced by mutation, this was an "origin of biological novelty".