So I think people's answers to your question will generally fall into three categories based on how tech orientated the company is and how big they are in general.
1. Companies that outright encourage open source work, perhaps even during work hours. I think quite a few FAANG companies are like this, and obviously the likes of Mozilla or Automattic would be as well.
2. Companies that disallow it/try to put limitations on what their employees can work on. Usually tech companies, though sometimes just large organisations in general.
3. And those that flat out don't care/don't control what employees do outside of work or don't know what open source is. My experience is that many agencies and mom and pop companies tend to be like this, as do those that are completely unrelated to the tech industry.
You can work on outside code projects, but they can't be related to the industry, help our competitors in any way, and we must get prior approval from the company.
I think most companies have restrictions like this. Your previous company seems a bit strict.