This is a difficult area - it can be hard to track usage for items that are open.
We wish that we could get this from Primo analytics, but it does not currently do anything with open access according to the Ex Libris documentation
There is an Open Access field in the Link Resolver subject area in Alma Analytics. Read more here
Currently, the best info is from your vendors. A couple resources:
Note that the instructions are slightly different for usage and title counts . . .