Sometimes we have a requirement to stop users from accessing a SharePoint Online site. For example, if there's an issue with data and we want a stable/non-changing site to work with we would like to stop users from accessing sites (Site Collections and/or sub sites) for a period of time while work is completed.
We could remove all users permissions from a site but that is a lot of work and then we have to reinstate the permissions exactly as before.
In on-premises scenarios we could put a Site Collection into read-only mode but that is not available to us in SharePoint Online.
Are there options available to us out-of-the-box?