Nintex workflow designer and Nintex forms designer looks for the servers running Microsoft Sharepoint Foundation WebApplication Service.

This also applies to Sharepoint 2016 and 2019 servers setup using Min-Role. If the server has this service listed as "Microsoft Sharepoint Foundation WebApplication Service" running , it is considered as a Web Front end and handles the user traffic and needs to be licensed. 

For example, if the workflow designer is loaded from a server running the Microsoft Sharepoint Foundation WebApplication Service and it is not listed on the Nintex workflow license then you would recieve an error that this server is not licensed.

This applies to Nintex Forms Designer as well. 

Here's a screenshot of Nintex Forms Designer being loaded from a server that is not listed on the License. 

Please note do not turn off this service "Microsoft Sharepoint Foundation WebApplication Service" in Production. Please talk to Microsoft Support  before making any major topology changes.

Applies to : Sharepint 2010 ,2013,2016,2019 

Applies to both  on-premises Perpetual and Subscription Licenses (Production only)