Generally, because the rollover was split between two different destinations, you would need to split the Form 1099-R for entry into TurboTax, one for the portion rolled over to the traditional account in the Solo 401(k) and the other for the portion rolled over to the designated Roth. However, it's impermissible to roll any distribution from a traditional account in a 401(k) over to a designated Roth account in a different 401(k). (See IRS Notice 2020-62 which explicitly states this.) If you choose to ignore that, you would just split the Form 1099-R as I mentioned, but there is always the remote chance that the IRS will detect the error and that could potentially disqualify your Solo 401(k).
What you should have done is to roll the pre-tax portion over to your Solo 401(k) and roll the after-tax portion over to a Roth IRA, not to the designated Roth account in your Solo 401(k). A rollover of the after-tax portion to a Roth IRA is perfectly permissible. In that case the code-G Form 1099-R would be the same and you would need to split it with one showing the pre-tax portion that went to the Solo 401(k) and the other for the after-tax portion that went to the Roth IRA.
