They own 15.1% of Fox's shares
Fintel summarizes the SEC filing:
2023-02-01 - BlackRock Inc. has filed an SC 13G/A form with the Securities and Exchange Commission (SEC) disclosing ownership of 45,743,746 shares of Fox Corporation - Class A (US:FOXA). This represents 15.1 percent ownership of the company. In their previous filing dated 2022-01-27 , BlackRock Inc. had reported owning 39,865,263 shares, indicating an increase of 14.75 percent.
Fintel tracks historical data. At the start of the pandemic, BlackRock owned 10% of Fox shares. As an investment company, they own a lot of shares in a lot of other companies.
For context, Investor.gov explains what 13D and 13G filings are.
Shareholders elect Fox's board of directors. According to Wikipedia:
The company is controlled by the Murdoch family via a family trust with 39.6% ownership share. Rupert Murdoch is chair, while his son Lachlan Murdoch is executive chair and CEO.