"You can contribute up to $69k combined from Employee and Employer if your employer allows it."
That's not the whole story because it does not address the limitations on employer contributions. One of those limitations is that the employer contribution is not permitted to exceed 20% of net earnings from self-employment, which is why your net profit would have to exceed $234,000 (somewhat more if you do not also have $168,600 of W-2 income subject to Social Security taxes) to be eligible to make a $46,000 employer contribution. However, you could make after-tax employee contributions, plan permitting, to bring you up to the $76,500 limit, provided that your net earnings are at least that much. Net earnings are net profit minus the deductible portion of self-employment taxes.
As I said, as far as I know, the IRS has not provided any guidance as to how to report the amount of an employer Roth contribution to an individual 401(k). Because it is not deductible, it could possibly simply be omitted from the tax return, but if you do so there would be no tax record of it and as a result there would be no checking against the 20%-of-net-earnings limit. By entering it as a deductible contribution and an IRR, that checking gets done. (I'll agree that the situation is a bit different with a sole proprietor than a separate employer and employee because the sole proprietor gets both the tax deduction for the traditional employer contribution and the income from the IRR cancel each other out on the same tax return, while with a separate employer and employee the employer's tax return shows the deduction and the employee's tax return shows the taxable income.)
