Why does Turbotax show that I can defer 23k as an employee in a self employed 401k plan, even though I maxed a 401k via my W-2 job (box 12 D and AA)?

My understanding is that the employee elective deferral limit is across all employers. Using the "Maximize Contribution to Individual 401(k)" option, it suggests that I can elect to defer another 23k in addition to an employer contribution (that matches what I get from other calculators).