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There could be the reason that custom scripts are disabled on root site collection for security reasons and due to that Script Editor, Content Editor web part and many other web parts or features are not available where user can add custom scripts. Follow the below links to active the custom script.
Please refer below link:
Missing web part and features in ...
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You'll need to get the admins to change the "allow custom script" setting. When this setting is off, it blocks a variety of features including the script editor part, as well as search web parts and many other features. The docs that have instructions for changing the setting, as well as the full list of features affected, is here.
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What do you mean the menu bar?
In the modern page, the search box is in the suite bar in the top of the page. It is by design.
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If search status shows as 'All Errors', there can be multiple reasons behind it. You can try following things to see if it helps:
Go to Windows services console and restart both SharePoint search service 15/16 and SharePoint search host controller one by one. Wait for sometime to see if helps.
Check in Central admin --> Application Management --> Manage ...
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You can't change file types from search index in Office 365 SharePoint Online. There is no setting to configure it in SharePoint Online Admin Center.
A similar thread: Sharepoint Online Office 365 Search custom file types index
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Neither of what you're asking for can be accomplished at this time. All search boxes are going to the top of the page, but the suite nav is not something that Microsoft supports manipulating -- any any customizations you would make will eventually break.
As far as redirecting it, that I believe is on a roadmap item to allow you to customize it but is not ...
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To allow custom script on a particular site collection immediately, run the following PowerShell with SharePoint Online Management Shell:
Connect-SPOService
Type: https://<yourdomain>-admin.sharepoint.com
Sign in with username and password
Set-SPOSite -Identity https://<yourdomain>.sharepoint.com -DenyAddAndCustomizePages $false
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