Mussolini wanted to flood Libya with Italian settlers so that it would be Italian majority.
As for Slovenia, he did engage in multiple ethnic clensings of Slovenians otl
The Italians planned to flood settlers into Libya. The didn't plan to execute or exterminate through labor 80% of the population.
Slovenia is actually an excellent example of the difference between Italian policies and the Reich's. Italy started out with no plans to cleanse any part of the population, but then vastly overreacted (as fascists tend to do) to resistance by putting tens of thousands of people into concentration camps resulting in thousands of deaths. Interestingly, prior to the surrender in 1943 the Italian fascist government had begun to reverse some of the policies seeing them as counterproductive in stifling dissent and resistance. The Reich walked in with a plan to simply murder 25,000 people to clear space.
It is impossible to compare ANY modern actions to GeneralPlan Ost. The GOAL was to liquidate 80-100% of various populations while outlawing the use of native languages in written form, leaving a sprinkling of the original population to work as illiterate slaves. The plans (there never was a finalized version since, like most everything the Reich did during the war, they were making it up as they went along) was breathtaking in their scope and the sheer vileness of the evil involved.
Fascist Italy was not, in any way, shape, or form, an innocent player, there were plenty of war crimes to cite. GeneralPlan Ost, however, is on an entirely different plane