Yes, you should add your Sec. 401(k) contributions to your wages for QBI. This is essentially the Modified Box 1 Method. The Unmodified Method would result in a lower amount (wages only); the Tracking-wages Method is useful only if you have more than one business.
See this article from the Tax Advisor for a clear discussion of the QBI wages topic: Computing qualified W-2 wages for Sec. 199A purposes.
Note that 401(k) contributions are reported on Form W-2 Box 12 Code D.
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