Thanks for pointing that out, paul35! I'm going to bring this up with my team to make sure QuickBooks Online is working as seamlessly as possible in these sorts of situations.

From doing tests in my own account, I saw exactly what you were saying. I was able to get the project to appear as an option for existing transactions after creating it by logging out of my account and back into it afterward. I recommend giving this a try if you have more transactions you'd like to move.

Great job with finding a workaround that got the job done for the time being! It's a good idea to double check your books to make sure you don't have any duplicate transactions now that you've used the Copy feature.

I'm here if you need anything else. :)