Purchased a condo in Delaware to live there, can I now file income tax fedral and state in delaware?

If you had no income from any source while a resident Maryland in 2019 then you would not file a Maryland state income tax return for tax year 2019.

did you rent while living in Maryland.   if you owned your residence there, what happened to it?

For Delaware, you are a part-year resident.  but it gives you filing options

Part-Year Residents may elect to file either a resident or nonresident return. 

Part-year residents electing to file a resident return – This option may
be advantageous if, during the period of non-residency, you had no
income from sources in other states and/or your only income was from
Delaware. Please refer to the instructions for Form 200-01 to review this
option..
Part-year residents electing to file a non-resident return – This option
may be advantageous if, during the period of non-residency, you had
any income from other states or sources outside of Delaware.

You became a Delaware resident for state tax purposes on the day you began living in your new home in Delaware.  Any income you received after that date (including any capital gain) would be taxable by Delaware.  If the income was or is received in 2019, you would file a 2019 Delaware tax return, as explained by @12309 .

Note: If the capital gain you refer to was from the sale of real estate located in Maryland, it would be taxable by Maryland - and also by Delaware, if you received it after becoming a Delaware resident.