Azure DevOps does not support SharePoint Team Sites (since 2018) - Discontinue SharePoint integration - TFS https://learn.microsoft.com/en-us/previous-versions/azure/devops/report/sharepoint-dashboards/deprecation/discontinue-pre-tfs-2017-sharepoint-integration?view=tfs-2017&WT.mc_id=DOP-MVP-33518.
When a prospect/client is ready to move forward (typically after a Specification Review)...
Figure: Choose to create a new SharePoint site when creating Azure DevOps project
Note: It is also possible to create a new SharePoint site afterwards and attach it to a Azure DevOps project, via this hack
A few other things to do frequently do right away:
Figure: Once your 'TFS Portal' is ready, add a picture of the team site, prior to letting them know about the new site