I'm unable to build stacked charts with the new dashboard chart builder. I put in a Support Ticket and this is expected behavior. I'm not sure I understand the purpose of removing functionality and weakening the chart build options.
Support's Response: You're right that the new chart widget behaves differently from the legacy one. Because reports in Smartsheet are dynamic and change based on their filter criteria, the "Build manually" option pulls in the entire report rather than letting you select specific data ranges. For the same reason, it doesn't support selecting multiple columns the way the older charts did, which is why you can only choose one field.
To create the stacked bar chart you're looking for you'll need to use the "Build Legacy Chart" option. This is currently the only way to chart multiple report columns together in a stacked format.
Sharing here in case anyone else is stumped on the same thing trying to build a chart like we've been able to do before in the new version. You cannot.
Separately — regarding the overlapping text when searching assets — they said this is a known UI issue and are working on it.