Regarding your state income tax, read this about "domicile."
https://www.marylandtaxes.gov/forms/Tax_Publications/Administrative_Releases/Income_and_Estate_Tax_R...
You can only have one domicile at a time. It is possible to be away from your domicile for a long time without changing your domicile, and changing domiciles requires active steps to abandon your old domicile as well as steps to establish a new domicile.
If you have abandoned your domicile in Maryland and established a new domicile in Germany, you don't owe Maryland state income taxes. But if audited, you will have to show the steps you took to abandon your domicile. That might include canceling your lease or selling your home, but you may also need to cancel your voter registration and drivers license, show that you changed doctors, etc. Hanging on to your MD drivers license and voter registration "just in case" could be used by Maryland to claim you did not actively abandon Maryland as your domicile.
