Unnie Ayilliath

There are many different business scenarios when we want to set a SharePoint site collection as read-only mode (as shown in above screenshot) to prevent any further addition/modification of content but simultaneously to make the existing content available to the users.

Using SharePoint Online Management Shell

Set-SPOSite -Identity “<SiteURL>” -LockState “ReadOnly”

Read more about other lock statuses here

Using PnP PowerShell

Connect-PnPOnline -Url “<SiteURL>” -Interactive

Set-PnPSite -LockState ReadOnly

Read more about Set-PnPSite command.