@Ovidiu Drăgan @Logicnet Solution ,
Normally, the People Picker control provides a "friendly" display of users or groups when a claim authentication is used.
And now we can disable the people search functionality used in the People Picker. The "friendly" display can be disabled by using the SearchResolveExactEmailOrUPN parameter of the Set-SPOTenant cmdlet.
With the feature disabled, in order to resolve names in the people picker, we must enter the user's full email address or User Principal Name (UPN).
This example disables starts with for all users/partial name search functionality for all SharePoint users, except SharePoint Admins.
#Variables for processing
$AdminURL = "https://tenant-admin.sharepoint.com/"
$AdminName = "julie@tenant.onmicrosoft.com"
#User Names Password to connect
$Password = Read-host -assecurestring "Enter Password for $AdminName"
$Credential = new-object -typename System.Management.Automation.PSCredential -argumentlist $AdminName, $Password
#Connect to SharePoint Online
Connect-SPOService -url $AdminURL -credential $Credential
Set-SPOTenant -SearchResolveExactEmailOrUPN $true
Note, recently resolved names will still appear in the list until browser cache is cleared or expired.
This also does not allow SharePoint users to search for security groups or SharePoint groups.
SharePoint Administrators will still be able to use starts with or partial name matching when enabled.
More information for your reference:
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