I can't find where to enter my balance forward on Cumulative Canadian Development Expenses from 2018 (formerly T1229). Any suggestions?

You would enter the amount on the T5013 slip page. To do this in TurboTax Online, use the Find tool (magnifying glass) to search for "t5013". Then select “T5013 - Statement of Partnership Income” from the list, and then click the Go button.