It's no secret that Safari is far less customizable than Firefox (for example), and if you want to achieve what you seek you will need to peruse the App Store for Apple's curated supply of potential solutions or workarounds:
https://apps.apple.com/us/story/id1377753262
I want to use Google search ...
For the life of me I have no idea why anyone would want to use Google search. I have no doubt Google used to be the best search engine, maybe a decade or more in the past, but today it's a joke. Unless of course you're looking for advertisements, or if 832,000 results in .003 seconds impresses you, or you just want to be brainwashed. That's what Google is best for.
... I don't want Google AI summaries.
Then you clearly need to contact Google for assistance. Seems to me though their AI - generated answer was half useful... as you already determined. I'm not sure it's even that much.
You really like Google search? You can install this Chrome Web Store extension that uses Startpage to conduct a Google search using the Brave browser:
https://chromewebstore.google.com/detail/startpage-%E2%80%94-private-searc/fgmjlmbojbkmdpofahffgcpkhkngfpef
Startpage performs a Google search, but it strips all extraneous personal information from the search query before returning Google's results to the Mac. Or, just set Safari's homepage to Startpage.com. Again, no need to use Chrome.