So are you saying that no members of McDonalds were part of the union? The union had absolutely 0 remembers at McDonalds? I understand that in Scandinavia being part of a union is completely separate from the company, and any collective agreement, but you still need to be a member if I’m not mistaken.

You very clearly don't understand the rules here. No you don't have to be a member, Obviously the union isn't part of the company, that would be weird and wrong. But in bigger companies, the unions have a right to have 2 members on the board. But you cannot force people to be members of a union, that is illegal. You can only force a company to follow the agreement between DA and LO, or you may negotiate your own terms as a company.

When you start a new company like McDonalds was at the time (early 80's), they can easily ask the people they hire if they are members of a union, and then not hire them if they are.
IDK if any were, and it's irrelevant except for the ability to receive compensation from the union in case of a strike.

I am not familiar with the second example, but it is absolutely the case that unions may step in and blockade a company that doesn't follow the agreement set between the union of the companies (Employers) that in Denmark is called Dansk arbejdsgiverforening (DA) and the united worker unions called LO.
If these agreements aren't met by any employer, unions may step in and make sanctions, boycotts and blockades, to get them to follow the rules, disregarding whether they have union members employed or not.