Hey Phil,
First, I assume you are referring to the ability to add widget indicators to a column visualization time series Performance Analytics widget, as documented in https://docs.servicenow.com/bundle/xanadu-now-intelligence/page/use/performance-analytics/task/creat....
To create an equivalent chart in Platform Analytics, create a time series data visualization. Select the Column type. Add both of the data sources, the one you want as a column and the one you want as a line. You will end up with two tiles in the Metrics section of the config panel, one for each data source. Then on the tile for the metric you want as a trend line, change the chart type to Line. See Chart options for multiple metrics. Note that you can do this for multiple table data sources, not only multiple indicators.
