Creating this post to try and compile information in a quick and concise format. User Voice information included.
*This end of life cycle does not affect SharePoint Server 2016/2019 on-premise farms.
8/1/2020 - SharePoint Designer 2010 workflow creation is turned off in new tenants.
11/1/2020 - SharePoint Designer 2010 workflows are being turned off. When they are turned off,
11/1/2020 - SharePoint Designer 2013 workflow creation is turned off in new tenants. 2013 workflows can be turned of via a PowerShell script, but I'm guessing you'll need to go through a Premier Support case to get it. There is no information published about this PowerShell script yet.
??/???? - SharePoint Designer 2013 workflows are being turned off. No published date for this.
Below are some links to review, in the User Voice link there were some users who reported filing a Premier Support case with Microsoft and received an extension to 3/1/2021.
Run the SharePoint Modernization Scanner. This generates some great reports that include how many steps are in the workflow and if the workflows have the potential to move into Power Automate. I've used this to help prioritize certain workflows over others, very helpful to identify the low-hanging fruit that is easier to update. Also, getting this information appears to be a requirement for the Premier Support case mentioned above.
License Information about Power Automate/Apps - https://go.microsoft.com/fwlink/?linkid=2085130 This link leads to a PDF that is revised on a regular basis. For more information about Power Automate licensing that is included with O365 Subscriptions look for "Power Automate use rights included with Office 365 licenses" as that section is not linked in the table of contents.
Article where Microsoft is updating news regarding this change - https://aka.ms/sp-workflows-support There is a section in this article that describes the symptoms of what you may see when SharePoint 2010 workflows are disabled on a tenant, so that will be very handy information.