This TIP I was about to share previously but then it slipped my mind.
Yesterday, One other Sharepoint Poweruser contacted me as he was having issues customizing the pages on Office 365 Group sites (Modern Team Sites) as well as Communication Sites using Sharepoint Designer but he was able to customize Classic SharePoint template sites.
This prompted me to write this short post so that if anyone else is facing the same issue can just use this TIP.
Here is the Reason and solution:
For Office 365 communication sites and group sites (Modern Team sites), add and customize permissions is denied for everyone by default but for classic team sites, it is allowed by default.
This permission allows to edit pages in SharePoint Designer.
If this permission is restricted, you will get access denied while making changes in site pages in Designer.
To allow this permission, below is the PowerShell command (make sure you launch Sharepoint Online Shell before executing below command)
Set-SPOSite “SharePoint site URL here” -DenyAddAndCustomizePages $false
Setting “DenyAddAndCustomizePages” to false allows designing or editing pages for user who have design or above permission.
Thanks for reading