A simple search on the web and you'll see that you cannot turn it off. see screenshots https://www.cnet.com/tech/services-and-software/ai-overviews-are-taking-over-google-search-how-to-turn-it-off/

You can mark this non-browser issue as resolved and have a nice day.

I don't know if this somewhat snarky response came from a human being or a bot. I hope it was the latter. I did search and search and search and I found many "solutions" for Firefox (both written and on YouTube) that didn't work in the end. I guess none of my searches were simple enough. That is why I wrote to you. I indicated the option of "browser" because I didn't know which one to choose when asked. Anyway, I hope you have a nice day, too. I didn't mean to waste your time, but no, my issue was NOT resolved.

This style rule will hide the AI section (tested while signed in, so results may vary):

div[jscontroller]:has(svg + span + div > strong),
div[jscontroller]:has(svg + span + div > h1) {
    display: none !important;
}
 

You can test by pressing Shift+F7 to open the Style Editor while view the results page, click the + button above the list in the left column to create a blank sheet, then paste the rule into the blank sheet.

Does that work on yours?

Obviously it's not practical to do that every time. Custom style rules can be applied using uBlock Origin (I don't know the specific syntax), or a general purpose page restyler like

https://addons.mozilla.org/firefox/addon/styl-us/

More details if relevant.