Use the theme drill-down. On an organization roadmap, each band has a control labelled Across products → — its tooltip reads “See [theme] across products”.
Click Across products → on the theme band you care about.
The board re-bands itself: instead of one band per theme, you get one band per product, showing that theme’s objectives in each.A chip appears next to the roadmap name — Theme: Retention and expansion ✕ — so it is always clear which theme you are looking at.
Note: the drill-down is remembered per roadmap, so if you come back later and the board is grouped by product with a Theme: chip showing, you are still drilled in from last time.