Can't change Safari homepage in High Sierra

Please describe the method you are using to change the home page in detail. Remember we cannot see what you are doing? Also, do you have any antivirus, cleaning or any other third party "maintenance" apps installed?

See this article Set your homepage in Safari on Mac - Apple Support

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turn of safari extensions .

In user library see this article macOS Sierra: Library folder

Delete the contents of folders caches , cookies , saved application state , search a folder preferences - delete com.apple.Safari.plist into the trash , restart the Mac then set the home page again , enter the correct web link in search engine field ( you can manually type or create a new tab - use command and T keys , search the web link for google or yahoo services , select it ( command and A ) , copy it ( command and C ) , switch to the home page window and paste ( command and V) in search engine field .