As far as I understand, it’s Congress running out of patience implementing the decision they made quite a few years ago, and which the FAA have pretty much dragged their feet on.
One cannot help being sympathetic to such frustrations, considering the ruling was established in 2018. But it’s been talked about since not long after 9/11, when the hardened doors were made mandatory.
A light-weight secondary barrier is already an option at Boeing and Airbus, including narrow-bodies. They have been installed since 2003, cost is around 5K USD per installation and there are hundreds of aircraft which have been modified.
https://www.alpa.org/advocacy/flight-deck-barriers