A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Dear SG523,
Sorry for the late reply.
As you want to use the built-in approval workflow in your environment which is a SharePoint 2010 workflow and the SharePoint 2010 workflow has been retied, you may be unable to use it. If you want to create the SharePoint 2013 workflow, you may use SharePoint Designer to create it.
However, for modern SharePoint libraries in SharePoint Online, the SharePoint 2013 workflow is also being retired and replaced by Power Automate. So there may be usage and data loss issues when the SharePoint 2013 workflow retires in the future.
I strongly suggest you use Power Automate to create the approval workflow in the modern SharePoint libraries. If you need further help on the Power Automate flow, please post back with the detailed information about your requirement and I'll try our best to help you on the flow requirement.
For your reference: SharePoint 2010 workflow retirement
Thanks for your understanding and have a nice day!
Cliff