Last December, Microsoft announced a name pronunciation feature, but administrators could not configure it via Microsoft Graph. The API returned an error or was not ready. During my tests, the default configuration was True, and the name pronunciation feature available to all my users.

Now, Microsoft has added the admin toggle in the Microsoft 365 admin center, meaning admins can configure the feature without PowerShell. The admin toggle should be available since Friday, 18 April.
Administrators can decide whether to display pronunciations that users set up in their profile cards. To enable the display of user-created name pronunciations, set the isEnabledInOrganization property of the namePronunciationSettings object to true. When this property is set to true, pronunciation is displayed for everyone within the organization. When this property is set to false, pronunciation not displayed for anyone within or outside the organization. The default setting is false.
Your account must be a Global administrator for the configuration. You can find it in the Microsoft 365 admin center > Org settings > Security & privacy > Name pronunciation.

Also, the namePronunciationSettings Graph API is now working.
In the meantime, the name pronunciation feature is no longer available for my users compared to last December. Microsoft changed the configuration. The API confirms that the configuration state is now False.
Import-Module Microsoft.Graph.Authentication
Connect-MgGraph -Scopes "PeopleSettings.Read.All"
$Url = "https://graph.microsoft.com/beta/admin/people/namePronunciation"
$Result = Invoke-MgGraphRequest -Method GET -Uri $Url -ContentType "application/json"
$Result

Admins can simply change the value to True (Enabled for all users) or False (Disabled for all users), as described in the documentation.
Connect-MgGraph -Scopes "PeopleSettings.ReadWrite.All"
$Body = @"
{
"isEnabledInOrganization": true
}
"@
$Url = "https://graph.microsoft.com/beta/admin/people/namePronunciation"
Invoke-MgGraphRequest -Method PATCH -Uri $Url -Body $Body -ContentType "application/json"