By default site creation is enabled and anybody can create a new site collection from SharePoint start page :

with two options: “Team site connected to an Office 365 group” and “Communication site”

SharePoint administrator might disable Sites creation. In Office 365 under SharePoint Admin Center -> Settings -> Site Creation there is “Let users create sites from the SharePoint start page and OneDrive”:

Under classic settings page -> Site Creation it is called “Show the Create site command” with explanation “Display the Create site command on the SharePoint home page and in the sites list in OneDrive so users can create new sites”:

If site creation is disabled, user will not see “+ Create site” in SharePoint landing page:

The fun part is users are still able to create a new Office-365 group based site collection
as “Let users create sites from the SharePoint start page and OneDrive” means literally “from the SharePoint start page and OneDrive” and does not mean you cannot create a site from other places. The same with “Show the Create site command” as it is literally about “Show…command” but not “disable … command”.

Option 1: from OneDrive, using “Create shared library”:

Option 2: using direct link:

Use Direct link: https://changeThisToYourTenantName.sharepoint.com/_layouts/15/CreateGroup.aspx
e.g.
https://contoso.sharepoint.com/_layouts/15/CreateGroup.aspx

Option 3: from teams:

and worth to mention that from Teams anybody can create a Team and a corresponding SharePoint site:

Unfortunately, if sites creation is disabled, you cannot create a communication site.

How to disable self-sites creation for real

The only way to limit self-site creation is using PowerShell:
– create a security group
– add to this group users who will be able to create sites
– via PowerShell Set-AzureADDirectorySetting command set “GroupCreationAllowedGroupId” property
Microsoft: “Manage who can create Groups“