Since this is being posted fucking everywhere with the same sensational headline that makes it look like linkedin is jumping out of the browser to scan your actual filesystems, here's an exerpt from the site linked:

The Attack: How it works
Every time you open LinkedIn in a Chrome-based browser, LinkedIn’s JavaScript executes a silent scan of your installed browser extensions. The scan probes for thousands of specific extensions by ID, collects the results, encrypts them, and transmits them to LinkedIn’s servers. The entire process happens in the background. There is no consent dialog, no notification, no mention of it in LinkedIn’s privacy policy.

It's enumerating the browser extensions you have installed.