I suppose a big ticket item like a car is much easier to boycott than 50 small items from the grocery where trying to search through the ownership tree for every conglomerate would use up the rest of my sanity
The good news (at least for the EU, don't know about non-EU European countries) is that groceries are only a blip on the radar when it comes to imports (of course, energy is used for groceries, but that applies both to European and US products) [1]:
[1] Of course, there are US conglomerates that produce in the Europe. But a good chunk (at least here) is Unilever, Nestle, etc., which are all European.
Looking at labels is hardly a test of your sanity. In Canada right now a majority of the population is regularly checking and avoiding anything made in the USA.
I was recently in Malaysia and they've boycotted certain American brands over the Israel-Palestine war. For example, KFC has given up and was shutdown everywhere. So boycotts can work.
Maccas seemed to be doing just fine though, take from that what you will
