You have until the due date of your tax return, including extensions, to make the employer contribution to the solo 401(k).
Regarding the employee elective deferral or Roth contribution, you were required to make the election to for these by December 31, 2022. If you made that election, you are supposed to make the deposit as soon as practical, but no later than the due date of your tax return, including extensions. Of course it's not practical to make the employee contribution until you are sure that you have the net earnings to support the contribution. Even if you didn't know the exact amount on December 31, your election by that date could have specified the maximum and your contribution would then be potentially limited once your net earnings are known.
(For 2023 and beyond, the SECURE 2.0 Act makes the deadline to make an employee election the due date of the tax return for new plans established by the due date of the tax return for that year, but that does not apply in your case because the contribution in question is a contribution for 2022 and in 2023 it won't be a new plan, so your election deadline will be December 31 of each year going forward.)
