DOOM: Eternal can be a challenging game, and the Marauder boss (your first encounter with this sort of enemy) represents both a critical story moment and one of the absolute toughest parts of the campaign. Many of the weapons, tactics, and techniques that you’ve learned up to this point in the game don’t serve you well in this fight, due to the Marauder’s defensive abilities and the extremely compact arena in which the battle takes place.
Source: N4G PC DOOM: Eternal: How to beat the Marauder