In short, SharePoint 2010 workflows in Office 365 are retired. The only supported way to create automation is Microsoft Power Automate (ex. Microsoft Flow).
| Date | Action |
|---|---|
| August 1, 2020 | SharePoint 2010 workflows will be turned off for any newly created tenants. |
| November 1, 2020 | SharePoint 2010 workflow services will be removed from existing tenants. |
More details can be found here.
Microsoft MVP & Office 365 Consultant Blog 