No, you cannot.
You will find this response from numerous sources with the search "roll Roth IRA to Roth solo 401k"
The IRS says so here:
" Roth IRAs can only be rolled over to another Roth IRA."
https://www.irs.gov/retirement-plans/retirement-plans-faqs-regarding-iras-rollovers-and-roth-convers...
You can also gather this interpretation from the law, and its description of qualified Roth rollovers:
https://www.law.cornell.edu/uscode/text/26/408A
see § 408A (e)(1). Rollover from IRA to non-IRA not a qualified rollover.
