An extension can store more than the browser it runs in

Clearing browsing data does not touch extension storage. That is by design, since an extension's data is its settings and saved content rather than your browsing history, and it means a single extension can quietly hold more than the browser's own cache.

Find the large ones

cd ~/Library/Application\ Support/Google/Chrome/Default 2>/dev/null
du -sh Local\ Extension\ Settings/* IndexedDB/chrome-extension* 2>/dev/null \
  | sort -h | tail -10

The folder names are extension identifiers, not names. To match one to an extension, open the browser's extensions page with developer mode on, where each entry shows its ID.

What extensions store

• Saved content. Read later tools, note clippers and password managers keep their own local database.
• Sync state. A local mirror of whatever the extension syncs to its own service.
• Caches. Ad blockers keep filter lists, which are updated frequently and are modest.
• Media. Screenshot and recording extensions can store captures locally, which is where the surprising numbers come from.

Removing it safely

1. Identify the extension from its ID on the extensions page.
2. Check whether its data syncs to an account. If it does, removing the local copy costs nothing.
3. If it does not, export from inside the extension first.
4. Remove the extension through the browser, which removes its storage properly.

The wider profile

Extension data is one part of a browser profile, and rarely the largest. The Chrome measurement found profiles well ahead of the cache, and every Chromium browser has the same layout, so the same check works in all of them.