RMD is not eligible for conversion to a Roth.  

The first dollars taken from an IRA after you reach age 70-½ are deemed by the IRS as going toward the RMD. Therefore, you must distribute the RMD before any amount of your IRA is converted to a Roth. Failure to do so could result in an excess contribution to a Roth IRA. The IRS levies a 6% penalty for each year this money remains in the Roth IRA.

The pro-rata rule applies to RMDs in the same way it is used for Roth conversions. For example, an IRA owner has an account worth $100,000, of which $15,000 is after-tax contributions. The owner is over 70-½ and has to take a $3,000 RMD before converting $20,000 to a Roth. 15% of the RMD ($450) is considered after-tax and 15% of the Roth conversion ($3,000) is after-tax.

https://rodgers-associates.com/blog/are-roth-conversions-right-for-people-over/