The upper limit to the mass that a main sequence star can have is not very well known.
There are probably stars as massive as 60 M☉, although they are extremely rare. More massive stars would be so luminous that the radiation they emit would push outward with a force rivaling gravity’s inward pull. Such stars would begin pulsating. The pulsations would begin small but would grow until they became so great that shells of matter would be thrown off the star. When enough material had been shed that the star’s mass fell to about 60 M☉, the star would become stable and resume its normal evolution.