When you try to add an Excel Web Access web part in SharePoint Online, you may not see the web part in the Business Data category.
In this situation, you have to activate the following features and options before the Excel Web Access web part is displayed:
SharePoint Server Enterprise Site features under Site Features.
Site Settings > Manage Site Features under Site Actions
SharePoint Server Enterprise Site Collection features under Site Collection Features.
Site Settings > Site Collection Features under the Site Collection Administration
Your custom scripting on the SharePoint tenant administration page.
https://<tenant>-admin.sharepoint.com > Settings > Custom Script > set both options to Allow.
Important The Custom Script options take 24 hours to activate after you set them. Therefore, you won't immediately see the Excel Web Access web part in SharePoint Online.