This is likely due to an extension you have running on your Arc. To resolve this, disable all extensions related to search engines, confirm you're able to access all search engines in your Arc Settings, and then one at a time re-add the search engine extensions and check to see if all search engines are still available.

Once you find the culprit, you'll want to remove that extension from your browser entirely to ensure this doesn't happen again.

Just in case, you can find these in the Mac menu bar under Extensions > Manage Extensions.