So the Executive branch gets zero say in how any of the Executive branch's property, building and assets is decided. That's certainly one way to look at it. Or one could argue that renovations are a routine function of any entity that manages PPE (Property, plants and equipment) as a part of normal asset management.

Hardly. The executive branch has a lot of say in how the U.S. government's property, building and assets are decided - because Congress has provided for that in statute. And they provide a budget for managing U.S. government property, all over the country and the world. Congress has authorized routine functions to operate and maintain property.

What Congress has not provided for is funding (either direct appropriation or authorized outside sources) for this project.

I mean, think about it in terms of what you described. Suppose you own a building, and have retained an asset management company. You obviously will delegate to that asset management company the ability to do routine repairs, maintenance, and ordinary upkeep - but you won't have given them the right to tear down 30% of your apartment building and build something twice the size, right? That's something that you would say is a decision that you get to make, not the asset management company.

It's amazing how quickly the democrats rally around the "the Constitution" when their guy isn't in office but then turn around rally around "I've got a phone and a pen, and if Congress won't act, I will" when their guy is.

No more amazing than how quickly the Republicans criticize the "if Congress won't act, I will" when their guy isn't in office, but then turn around and rally around acting without approval when their guy is. It's a common feature of politics.

Objections to the ballroom and event space renovations are largely asinine.

They're not. This is Congress' call, not the President's - for a lot of very good reasons.