Hello @elesiuta,
This is a very interesting looking snap, but to my eye it just doesn’t meet any of the supported categories for classic confinement unfortunately.
I think in this instance there is no quick solution, but for your application to work as a confined snap you will need to work with members of the snap community and the snapd project to see what specific amendments might need to be made to an existing interface, or even the creation of a new interface, to allow for the fanotify_init() and other functionality you need.