Exception: Access denied. You do not have permissions to perform this action or access this resource (4235705)

When migrating from SharePoint On-Premises to SharePoint Online (Modern sites) and got the following error:

• This "AddandCustomizePages" permission is related to the scripting capabilities in sites and pages of Microsoft 365.

• For security purposes, scripting is not allowed on sites users create themselves, on modern team and communication sites, and on the root site for your organization by default.

• Click here to see how can change the custom script setting globally in your Microsoft 365 Admin Center to apply to all future sites in your tenant.
• To allow custom scripting on an existing SharePoint site:

1. Download and Install SharePoint Online Management Shell

2. Run SharePoint Online Management Shell as an Administrator

3. Execute the following commands to enable the AddandCustomizePages permission level on the site collection in Office 365, then attempt the migration again:

Connect-SPOService -Url https://domain-admin.sharepoint.com

Set-SPOSite https://domain.sharepoint.com/sites/SiteCollectionName -DenyAddAndCustomizePages 0

Note: Replace domain and SiteCollectionName accordingly, for example:  Connect-SPOService -Url https://metalogix-admin.sharepoint.com and Set-SPOSite https://metalogix.sharepoint.com/sites/Support -DenyAddAndCustomizePages 0