Hi anonymous user,
According to my research and testing, I agree with BhanuKiranMSFT-5847's answer, we cannot access "Search settings" in SharePoint Online using Graph API.
I suggest you can propose a feedback on this issue, Many features of our current products are designed and upgraded based on customers’ feedback. With requirements like this increase, the problem may well be released in the future. Thanks for your understanding and support.
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