Earlier quoted context omitted.
Picketing has been legal for a long, long time. There's no law now that says I can't go out and picket on the sidewalk outside Whole Foods or Walmart.
The commenter is referring to what's called a "secondary strike". These are heavily regulated under current law ( https://www.nlrb.gov/about-nlrb/rights-we-protect/the-law/se... ) and the PRO act would repeal these rules.
It's legal right now, even as clarified in the link you provided, to encourage a boycott of a struck product at a retailer. What's not legal is organizing a boycott of a whole store because they are stocking one or a few products from a supplier whose products are struck. That is, unless it's a company store that is the same employer as the producer of the products for which production is under a strike.