There's the theoretical risk of patent infringement that this post addresses, but the more important point (imo) is that the current state of affairs is stopping React adoption for teams that, without the input from their careful lawyers, would gladly adopt it. Or the fact the ASF legal team banned this type of license as a dependency for any of their projects.
You could, if you wanted, fork the original Apache v2 licensed version that didn't contain the PATENTS file. (Although as per the linked article, why would you want to?)
The point being that even in the extremely, vastly unlikely case that things would progress to an actual patent infringement suit that you lose, in the end, it may not matter, based on:
And even if Facebook could assert a valid patent protecting React, the damages are very speculative. I cannot find a case awarding a judgement for infringing a patent otherwise licensed through open source, but it’s not a case I’d want to file. “Hey Juror #2, please award my client Facebook money because we pulled a patent license that’s otherwise granted to millions of other people free of charge.”