Based on the new MS release, both existing and new groups will now get a SharePoint Online team site. Within a group’s team site, this roll out brings a new home page, features News for highlighting important content in the team, and the Activity web part for showing recently active content.
However, if you create a sub-site(using OOB “Team Site” template) under this Modern Group’s Team Site, the default landing page for the sub-site is created with the Classic SharePoint look and feel.
This results in an inconsistent end user experience where the top level modern site has modern homepage whereas the sub-site has classic homepage.
As of now, creating subsites with GROUP template is not possible through out of the box functionalities.
However, there is workaround using Dev PnP PowerShell cmndlets to create sub-sites under Group site with the Modern homepage as default landing page.
Link to SharePoint / Office 365 Dev PnP PowerShell CmdLets: https://github.com/SharePoint/PnP-PowerShell.
To install the PnPPowerShell Online Module:
1. Open SharePoint Online Management shell and install SharePointPnPPowerShellOnline module through this cmndlet.
2. Then update the module, Update-Module SharePointPnPPowerShell*
3. Use this cmndlet to check the installed PnP-PowerShell version, Get-Module SharePointPnPPowerShell* -ListAvailable | Select-Object Name,Version | Sort-Object Version -Descending
To create a new subsite under an O365 Group site:
1. Connect to your O365 Group site using this command, Connect-PnPOnline –Url <URL of the O365 Group site> –Credentials (Get-Credential); provide the Administrator credentials.
2. Use this cmndlet to create a new sub-site with Modern homepage, New-SPOWeb -Title "<title>" -Url "<url-suffix>" -Template "GROUP".
a. Example: New-SPOWeb -Title "MyGroup" -Url "mygroup" -Template "GROUP"
This creates the sub site with Modern look and feel.