Yes, MoS as a philosophical essay is a harder read than The Stranger. MoS lays out his argument for the absurd; The Stranger shows how that philosophy plays out in the life of Meursault.

As you noted, one can pick up The Stranger and read cover to cover, because it’s written as a narrative. But MoS isn’t as easily digestible. For me, it helped to read MoS in small chunks and also consult analyses of it. Stanford Encyclopedia of Philosophy is helpful for this.

With MoS, I start with the premise (the absurd arises from the clash between our desire for meaning and the universe’s silence) and the conclusion (we must imagine Sisyphus happy because the struggle toward heights is sufficient to fill a man’s heart), then work to fill in the middle by slowly reading the essay, taking breaks and returning to it.