If enough people do it then yes it will hurt companies or whatever you are boycotting.
On a personal level it can help you, as you know that whatever it is you are buying at least doesn't support whatever it is that you are boycotting. I boycotted Chinese products once due to the Uyghur genocide thing I then believed in, and it felt good knowing that I wasn't funding a thing which I thought to be wrong.
If enough people do it then yes it will hurt companies or whatever you are boycotting.
On a personal level it can help you, as you know that whatever it is you are buying at least doesn't support whatever it is that you are boycotting. I boycotted Chinese products once due to the Uyghur genocide thing I then believed in, and it felt good knowing that I wasn't funding a thing which I thought to be wrong.