I find this site to be useful:

https://www.efile.com/efile-maryland-income-tax-return-file-md-state-taxes-forms-refund/

"Maryland State Tax Return forms for Tax Year 2019 (Jan. 1 - Dec. 31, 2019) can be e-Filed with your IRS Income Tax Return until October 15, 2020. Oct. 15 is the 2019 Maryland return filing and electronic filing deadline. If you owe MD or IRS Taxes and you filed an extension, don't miss this due date so you can avoid late filing penalties. If you have not filed your Federal or State 2019 Tax Returns, you can e-File them until Oct. 15, 2020."