People are always so laser focussed on the latest trendy thing, but why not just boycott all huge corporations/organisations? It’s a much simpler rule that achieves the same thing and you have the added benefit of boycotting companies that haven’t had their corruption uncovered… yet!
I find it more effective to say, I'm avoiding product X for Y reason.
This starts a conversation more effectively with contacts rather than go full large company avoidance which is difficult for people to imagine, let alone act on.
I sympathise with what you're saying though.
This is actually addressed on the BDS movement website
https://bdsmovement.net/what-bds
Effective boycotts work on companies that are large enough to be noticed but small enough for boycotts to have an effect, while divestments and sanctions can be lobbied for larger institutions and governments.
I think just saying something like "why not just boycott all huge corporations/organisations?" can be a bit disingenuous when I think it's pretty well acknowledged that We Live In A Society that makes completely separating yourself from large corporations essentially isolate you from society as a whole