The total additions to your 401(k) are not permitted to exceed your net earnings, $20,445 in this case. TurboTax only enforces the overall elective deferral (section 402(g)) limitations, not the earnings-based total additions (section 415(c)(1)(B)) limitation. You'll have to enforce that limitation yourself by limiting your total additions to $20,445.
Note that your Roth 401(k) contributions don't get reported anywhere on your filed tax return (except, perhaps, in conjunction with a Retirement Savings Contributions Credit on Form 8880). Overcontributing does potentially disqualify the 401(k).
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