On June 24, the Democratic National Committee said that most delegates to the national convention will vote remotely, instead of being physically in Milwaukee. See this story.
As far as is known, the only U.S. political party that will have chosen its 2020 presidential nominee via an in-person presidential convention is the Republican Party.
On June 26, the party announced plans for four virtual hearings to help write the platform. See the party’s webpage here.