Hello. I was wondering how could I do different aovs for volumes like an height mask with or a mask based on a noise with karma, etc...
I have been trying by myself but I dont find the answer.

The short answer is that there is a karma aov node you can add to a karma material. It’ll feed any input in as a custom aov.

The long answer is that USD doesn’t support material based aovs. It generally expects either an LPE expression or a primvar. You can add custom aovs using either by using the additional render vars node.

The karma aov node that sidefx built to get around this limitation in the usd specs.