No, don't enter your 457(b) plan contributions under Deductions & Credits. Your 457(b) contributions are shown in Box 12 of your W-2 with code G, so you only need to enter this information on the W-2 screen.
Please see the FAQ below for instructions on how to enter the W-2 Box 12 information in TurboTax.
How do I fill out the Box 12 information from my W-2?
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