Hello,
how about a data sample with 3 to 5 projects and a manually mocked up chart using the drawing tools?
Charting soooo depends on the underlying data that it's really hard to show how to do things without context.
Conceptually, if you want to have gaps between stacked bars, then you need these to be data in the source table and format these data points to be invisible.
In this table, the source data shows a date as a start date, then the number of days for project phases and the number of days for gaps between project phases. These numbers may need to be derived with formulas from elsewhere in the spreadsheet, subtracting Start Date from End Date to arrive at the number of days.