Web Designer Galleries section is missing on SharePoint Online
So here are the steps for resolving the issue.
Step 01: Go to Admin panel
Step 02: Go to SharePoint admin center by selecting SharePoint from the left navigation
Step 03: There go to the setting page
Step 04: From there allow Custom Script
There is a note saying “changes to this setting might take up to 24 hours to take effect.” So here is the power shell command to do that for immediate effect.
Step 01: Open the SharePoint Management shell
Step 02: Type the below command to connect with SharePoint Admin Center in management shell. You have to replace your admin center url which is in line 1.
SharePoint Team Lead , Office 365 consultant