Hi Bondie.
If you want to share your desktop flow with your colleague, you can do this through emea.flow.microsoft.com, as you already suggested.
There are however two things that you need to be aware of.
1. Make sure that you share this flow within an environment that your colleague also has access to.
2. If you make your colleague a co-owner, and he wants to find the flow on the online portal, the flow cannot be found under the "Shared with me" tab but will be under the "Desktop flows" tab instead (co-ownership will be shown under the access column). Within the PA Desktop app, the shared flow will be found under the "Shared with me" tab.
If my info was not of any help, maybe this article on the Power Automate portal might be of further assistance.