You are a part-year resident of Delaware if you were domiciled in Delaware for part (but not all) of 2020.
Even if you were not domiciled in Delaware in 2020, if you spent more than 183 days in Delaware in 2020 and maintained a place of abode there, you are considered a resident. This means you should choose full-year or part-year resident for your residency status.
Part-year residents will be given the choice to file either a resident or non-resident return.
Note that students and military members have different requirements.