Is it possible to select elements in the Revit UI with the dynamo player, similar to the function of a watch node?
I have found this topic Can't select Element's ID in Result (Dynamo Player) without a proper answer.
Sure is. Check out the spring node package, there is a node called Springs.SelectInRevit. Just feed in the elements you want to be selected and it should work.
The idea has not been implemented still as per my knowledge.
You can vote here for the idea:
https://forums.autodesk.com/t5/revit-ideas/element-id-s-selectable-in-dynamo-player-output/idi-p/8531601

