Yes the IRS rules allow for both Roth Solo 401k and Roth IRA contributions in the same year/same time.
Tax year 2019 Roth Solo 401k & Roth IRA contribution limits:
For Roth Solo 401k, $19,000 made if under age 50. If age 50 or older, you can contribute an extra $6,000 catch up amount for a total of $25,000.
For Roth IRA, $6,000, or $7,000 if age 50 or older.
COMPLIANCE NOTE: Both Roth Solo 401k and Roth IRA contributions are not tax-deductible, but contributions and earnings are both tax free when distributed provided the distribution rules are met.
COMPLIANCE NOTE: Roth IRA contributions are limited if your income exceeds a certain amount. For that limit CLICK HERE.