I'm not talking about boycotts in general, like say the Montgomery Bus Boycott, because we know those can work. I'm talking about "Company that sells product made me mad" boycotts.
Whether it's past ones like the infamous Call of Duty: Modern Warfare 2/Left 4 Dead 2 boycotts, or more recently like the brewing chud Pride Month boycotts (And if we're being brutally honest here on the flipside: The all-but-in-name boycott of that Harry Potter game a month or 2 ago), all of them seem to universally fail spectacularly and not impede their targets in any way.
if workers are on strike and ask for boycotting like all the john deere and frito lay shit a couple years ago that can help, although what probably helps more is other organized labor refusing to ship, stock, or maintain products of companies trying to screw their employees.
During the ufw grape boycott, the consumer boycott was more for spreading public awareness. The real boycott was by the ILWU waiting until the grapes spoiled to move them.