One of my site collections the web part categories are missing for our users. Does anyone know what setting needs to be turned on so the web part category folders show up?
Please go to Site Settings > Web Designer Galleries > Web parts then Library tab > Library Settings > Permissions for this gallery and Check permissions.
You need read permission to see the Web parts.
Besides, activate SharePoint Server Enterprise Site collection features.
Go to site settings > Site collection features and activate it.