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Mage hand lack the ability for fine manipulation needed to untie anything except knots that are intended to be untied with a single pull.
Also it's might be hard to point a finger on a rope that binds you.
I don't see anything in the Mage Hand description that would suggest to me that it lacks fine manipulation, nor do I think untying knots requires that fine of a manipulation.
I recognize that Mage Hand can't use skills through it (or else one of the Arcane Trickster's main schticks would be pointless), but Use Rope isn't a skill anymore.
I also think that it would be really easy to point your finger at rope that was tying you up, unless they somehow tied each of your fingers down, too. It says, "point your finger" not "gesture strongly with your finger, hand, and arm outstretched fully" or whatever.
And I think Prestidigitation could do it as well.