The benefit of spreading information about companies to boycott is that with a collective effort, you can demonstrate that what this company has done is unacceptable. Many people will withdraw their support as a result.
Indeed, it’s evident that this approach has been effective, as many people have rightfully ceased buying products from numerous companies that back Israel. I’m only providing two examples for now, but there are plenty of other instances of this.
You’re absolutely right. Disposing of products you already own, like a shirt from Puma or your HP laptop, won’t have any impact at this stage. What you should do is refrain from endorsing or purchasing these products moving forward. Buying these products now, regardless of what you do with them, will still contribute money to support the companies.