Leronlimab doesn't target the spike protein; it modulates the immune system. The way racehorses have blinders to allow them to focus... this is Leronlimab and lymphocytes are their steeds. The only way it won't work is if your immune cells have no CCR5 receptors, which is rare.
Actually, there could be a severe mutation of CCR5 and that might cause an issue. But the virus can mutate all it wants and LLMab will still corral the immune system.