how to enter a RMD withdrawal?
See this FAQ.
Assuming you've set the Tax Attributes of the retirement account … it's just a transfer from that account to a taxable account.
IF you're having any taxes withheld from the w/d, those must be recorded in the taxable account or Q's tax reports won't see them.
SO, record the transfer for the full amount into the taxable account and split that transaction to show the full amount transfer and a Negative amount for the taxes (multiple lines if State taxes are w/h also).
Then, in the split window, click the Adjust button to reflect only the Net amount in the taxable account register.