> In a merger of this scale all the big powers (US, EU, China, and I assume also UK now) have basically veto right.

> There are countless examples where country 1 has stopped a merger between a company from country 2 and one from country 3.

From what I've seen, the only method of enforcement for a third-party country is to ban the sale of goods in their respective markets following the merger (like GE/Honeywell in the early 2000s). Would that even be possible in this case?

Not sure how this is enforced. Generally the merger falls apart if there are any indications of this happening.

Don't forget that these are public companies and a stopped merger can affect their stock. Besides, major investors would eat the board alive if they put the company in such situation.