It appears to be true that Disney's stock has taken a hit following the cancellation of Jimmy Kimmel's late-night show, but the phrasing of the claim is a bit misleading. It's important to note that a company doesn't lose money when its stock value changes. The investors who own it lose potential value if they sell now versus before (when the price was higher). Most people can simply hold onto their stocks and wait for the price to go back up. As for actual revenue loss, that's hard to know until Disney releases quarterly reports. Therefore to say that "Disney lost $4 billion due to..." suggests that the company has lost the money and that the value can't be recouped over time.
Snopes' fact-check on the matter roughly aligns with the dollar amount and timeframe. They report that "by the end of the week on Sept. 19, with its stock price at $113.76, Disney's market capitalization had fallen by $4.2 billion, or 2.5%, to $204.7 billion." Al Jazeera reports that "Between September 17 (when Kimmel's show was announced to be canceled) and early on Tuesday, the value of The Walt Disney Company's stock fell by 2.39 percent – the equivalent of $4.99bn of its market value." This dollar amount is higher than the original claim, but this covers a span of 7 days, not 4.
As for subscription cancellations contributing to Disney's losses, we just can't be sure. While there have been plenty of anecdotal social media posts of people canceling their subscriptions, Yahoo Entertainment notes that "there's currently no official metric to show just how many people have dropped the streamer since the Jimmy Kimmel news was revealed."
