AITA For Reporting a Coworker's Productivity?

Recently my job has created rules and policies and taken away OT. Previously it was the wild west and as long as we got our work done we could do whatever and have an abundance of OT. We were always ahead of the ball. Tensions are high and we are falling behind each day. This all resulted from an employee stealing time and being fired. I wound up with a raise and more responsibility.

Enter new supervisor M. He generally is a good guy, but is a bit overwhelmed and doesn't have the time to manage productivity of the warehouse as he learns our business. This is one of his tasks and a main reason he was hired.

Recently a coworker S has been unproductive while we fall behind. He milks the simplest tasks for the first half of the day and then checks out for the last 3 hours on his phone. Meanwhile the rest of us are trying to complete tasks in hopes we can get OT again and falling behind due to the nature of logistics in the world currently.

Daily I hear my coworkers gripe about S. They want me to bring this to M. I gave him the benefit of the doubt, people have bad days or weeks,but after nearly a month it has not subsided. Normally I would bring this to a coworker's attention, but S has a history of aggression and bullying. I brought some evidence to M and told him he could observe him the last few hours of the day and make a decision.

M immediately approaches S. They converse a while and S sits on his phone the rest of the day. On his way out S calls my name and says something I couldn't quite make out. His body language and tone didn't seem friendly. From what I gathered he said,, "Hey OP I DID MY WORK TODAY!!" It wouldn't be the first time he got aggressive or taunted someone for criticism.

AITA?