The use of Microsoft Viva requires using a modern SharePoint site as a home site.
The documentation for enabling Microsoft Viva describes how to set a new SharePoint Online Home Site, but lacks an important step.
You must swap the new home site and current home site, in addition to setting the SharePoint Online home site. The swap cmdlet archives the current home site.
# Replace with the new home site URL
$NewHomeSiteUrl = 'https://varunagroup.sharepoint.com/sites/Varuna'
# Replace with current home site URL
$CurrentHomeSiteUrl = 'https://varunagroup.sharepoint.com/'
# Replace with an archive URL
$ArchiveUrl = 'https://varunagroup.sharepoint.com/sites/oldhomepage'
Invoke-SPOSiteSwap -SourceUrl $NewHomeSiteUrl -TargetUrl -ArchiveUrl $ArchiveUrl