Forum Discussion
Is it possible to disable subsite creation in a modern team site?
You can turn this off for the entire tenant in the SP admin center. Settings>Subsite Creation.
Here's the text from the setting:
Control whether site owners can create a subsite in a site that includes an Office 365 group. This setting determines whether the option to create a subsite is available on the Site contents page when users click New.
I have used this tenant setting to turn it off ("Hide the Create site command") but it does nothing. Site Owners with Full Control are still presented with the 'new subsite' command, and are able to create one. Even on newly provisioned site collections (created after I configured this setting). Maybe I'm missing something, but it seemingly takes no effect throughout my tenant.
It seems that settings in the classic Admin site don't impact modern sites very often. In the new admin center you can disable the overall creation of sites but it doesn't have a subsite creation feature (YET). I would expect to see it there because you can also see Groups in this admin center while you can't do that in the classic. It's really a transition phase from Classic SP Admin center to the New Admin center.