@jalejandroc2928 the requested system-files access is far to broad - and basically is just equivalent to the access provided by system-backup. Also note that snaps run within their own mount namespace which is not the same as the host system - as such /usr and the like within the snap come from the base snap, not the real host system - and so even if you use system-files to try and access /usr you only get access to the /usr of the base snap, not the host system.
Thus it would be much better in-my-opinion to root all searches within /var/lib/snapd/hostfs/ and then when the snap wants to present these results, remove the /var/lib/snapd/hostfs/ prefix from them.
Finally, classic-support is a deprecated interface and should not be used.