Need help summarizing the date

If you don't need the time part of the order date for anything else then get rid of it. In Power Query change the type to be date rather than date time. Its important that you change the type in Power Query and not just in Power BI Desktop, as otherwise it will retain the time information.

If you do need the time part for other reporting then create a new column in Power Query by extracting just the date part, and use the new date column to link to your date table or in your visual.

Do as johnt75  said. Even if you use a separate dates table and relate it to your fact table, you'll only see blank rows because the relationship is between a date column and a datetime column. Splitting a datetime column into separate date and time columns or keeping just the date can reduce the cardinality and improve the efficiency of your data model.