On the manual Connect Core 6UL SBC Pro doc
https://www.digi.com/resources/documentation/digidocs/90002285/#task/digi-ade/t_download-install.htm#Install
the link below is broken, get 404:
Install Digi Application Development Environment
The Digi Application Development Environment for Linux installer includes:
Eclipse IDE for C/C++ Developers (https://www.eclipse.org/downloads/packages/eclipse-ide-cc-developers/oxygen1a):