I’ve worked in unionised industries in two countries and neither required union membership, it was optional.

I can’t speak for everywhere though. Maybe you can provide a reference showing that your local legislation works this way?

It seems to me you were supporting the op when he said

>It could be nice if companies would be forced to set up collective workers representation entities when they reach a certain numbers of employees, where I am the limit is of 50 employees, then you must have a collective representation

So if that was the case, how can I work for a large company without such workers representation?

What the OP is describing is that the company must provide a way for it's staff to join a union that they recognise. The individual staff members are still free to choose whether or not they want to join.