The distribution of these funds from the solo 401(k) will have code E (instead of code 1, 7 or G), indicating that the distribution was not eligible for rollover despite the funds having been rolled over to the Roth IRA. This Form 1099-R should show the distribution as nontaxable unless there was a gain while in the solo 401(k), in which case the gains will be taxable.
If you filed your 2021 tax return or requested a filing extension by April 18, 2022, you have until October 15, 2022 to obtain a return of the excess Roth contribution. The amount distributed will be adjusted for investment gain or loss. Since the excess Roth contribution was made in 2021, the 2022 Form 1099-R will have codes J and P in box 7, the amount distributed in box 1 and, if there was an investment gain, the taxable gains in box 2a. The amount in box 2a will be subject to ordinary income tax and, if you are under age 59½ at the time of the distribution, to a 10% early-distribution penalty. This is all reportable on your 2021 tax return, not on your 2022 tax return. Make sure that there you decline any tax withholding.
If you are late in filing your 2021 tax return (did not request a filing extension), on your 2021 tax return you'll owe a 6% penalty on the excess Roth IRA contribution and you'll need to make a regular distribution (code J, T or Q) of the excess, reportable on your 2022 tax return.
