I've heard from my peers at Meta that you should post a lot on Workplace, otherwise it can reflect badly on your PSC. Is this true or more of a myth?
Your peers are not wrong - Regular Workplace activity is effectively required for good performance at Meta. There are some scenarios where this isn't true:
That being said, it's not like Workplace is just some arbitrary chore you need to get PSC points, it's just crucial for effective communication and alignment in general. Meta is a company that heavily values communication ("Be Open" is literally one of its 5 core values), and Workplace is simply one of the best tools in the world to facilitate this. I remember not being sold on "Facebook for work" when I joined the company (I barely use Facebook personally), but I came to really understand the value it provides.
As an E4, you need to push for E5, which will require strong ownership of projects. At the always chaotic Meta, project alignment is always a big problem, so I heavily recommend getting good at writing effective Workplace posts ASAP.
Here's some resources to help you with that: