According to https://developer.chrome.com/docs/extensions/develop/migrate... the message is this:

June 2025: Chrome MV2 deprecation enterprise rollout

People will do anything not to get eating, except getting rid of the beast.

On macOS:

  # defaults write com.google.Chrome.plist ExtensionManifestV2Availability -int 2

This will continue to allow MV2 extensions for your Chrome instance. Confirm the policy has been set by checking chrome://policy. See [1] for possible values.

Now, because uBO is now disabled in the Chrome Web Store, you also need to install it as a "forced extension" (the way extensions are deployed in enterprise environments). Install the extension according to the section "Use a preferences file" in [2]:

  - Create a file named cjpalhdlnbpafiamejdnhcphjbkeiagm.json
  - Place it in ~/Library/Application Support/Google/Chrome/External Extensions/
  - With content:
  { "external_update_url": "https://clients2.google.com/service/update2/crx" }

You'll need to create the "External Extensions" directory, set file permissions according to docs, restart Chrome. The file name contains the extension ID to be installed, which you can verify from the submission URL of this post. Upon Chrome restart, it should notify you with a message in the top right that an extension was forcibly installed.

The ExtensionManifestV2Availability definitely still works for now, but it's been a about a month since I used the preferences file way of installing the extension on a new device. YMMV.

[1] https://chromeenterprise.google/policies/#ExtensionManifestV... [2] https://developer.chrome.com/docs/extensions/how-to/distribu...