"Can I convert RMD funds into ROTH IRA?"
A Roth conversion is defined in the tax code as a type of rollover, and rollover of an RMD is not permitted.
What you can do is use the cash from an RMD to fund a regular Roth IRA contribution, subject to the limitations on eligibility to make a regular Roth IRA contribution as would be the case with cash from any other source.
The following IRS webpage addresses eligibility to make contributions:
https://www.irs.gov/retirement-plans/plan-participant-employee/retirement-topics-ira-contribution-li...
