Hi @Anonymous,
You can leverage the out of box WinOpportunity unbound action in Dynamics 365. The Dataverse connector has a Perform an Unbound Action step you can add and pick from a list of available actions in the environment.
Note there is some known complexities/challenges when working with actions that have an entity reference parameter type. This requires you to manually set the Json object, in this case is the related Opportunity that you want to close. Hopefully MS addresses this in the near future to make bound/unbound actions easier to work with in the Power Automate designer.
This blog post describes this complexity in depth and provides examples of how to run some of the actions (I asked the author to provide one for WinOpportunity specifically earlier, so you should be able to get yours working).
---
Please click Accept as Solution if my post answered your question. This will help others find solutions to similar questions. If you like my post and/or find it helpful, please consider giving it a Thumbs Up.