how to enter MQ506NRS real estate sale information on non resident MD 505 form

It depends. If you are trying to enter the estimated tax withheld at the time of the sale for a Maryland (MD) property, it would be considered an estimated tax payment.

MQ506NRS: This form is used to determine the amount of income tax withholding due on the sale of property and provide for its collection at the time of the sale or transfer.

1.) Open/continue your tax return.
2.) You can either go to the Federal section, then Deductions & Credits or search for estimated tax payments and select the Jump to in the search results.
3.) Select Estimates and Other Taxes Paid.
4.) Next to Estimated Tax Payments, select Start or Revisit.
5.) Choose Start next to the type of estimated tax payment you'd like to enter (State)
6.) Enter the amount of estimated tax you paid at each of the quarterly due dates.

7.) Continue to complete the section - this will carry to your MD return