Yes, you can attach the Federal MFJ return to the state/DC return.
Please see this help article for instructions on filing joint Federal and separate State returns.
Although state returns can be e-filed with your federal return (or after your federal return has already been accepted), it's no longer possible to e-file state returns before the federal.
This adds an extra layer of security to all e-filed state returns. This also means you won't be able to e-file your state if your federal return was, or will be, paper-filed.
If you e-filed your federal return as Married Filing Jointly, but want to file your state returns as Married Filing Separately, only one state return can be e-filed. The other will have to be paper-filed.
Federal returns are not affected by this security measure and can be e-filed with or without a state.
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