Problem
One our site collections in SharePoint 2016 farm was in read only mode. When I navigate through Central administration the options under Site Collection Quotas and Locks are greyed out and I was not able to change the options.
Solution
To remove the read only I ran the below PowerShell script and it worked.
$site = Get-SPSite "siteurl"
$site.GetType().GetProperty("MaintenanceMode").GetSetMethod($true).Invoke($site, @($false))
