Tack “&udm=14” on to the end of a normal search, and you’ll be booted into the clean 10 blue links interface. While Google might not let you set this as a default, if you have a way to automatically edit the Google search URL, you can create your own defaults.
But even activated, results don’t default to an AI chat, that’s a different beta page you have to go through intentionally. I’ve never noticed the Assist because I’m not in an English speaking region and it is not available at all for me. But the point stays, they don’t use Microsoft’s AI. They use GPT-3 and Claude.