Can you please expand on that last line? I read it two ways and I'm not sure which one you mean.

Does the "you can't do that" refer to getting a how-to-build-a-wormhole recipe from general relativity, i.e. "I can't tell you how to build one, go figure it out yourself".

Or is it more along the ways of "You don't have a worm hole? Well too bad, there's no way you can create one. But hey, it could totally hypothetically exist."

If it's 1) then we could possibly build one (or find it in the universe somewhere) and GR just doesn't tell us how. If it's 2) then we know it can't even be created.