Nice little tutorial!
In OnShape one can have multiple “parts” in one Part Studio. I export the entire Part Studio (right click on the tab and select export) as STEP and add that to a plate in Bambu Studio (too many “Studios”!), selecting not to break it up (same dialog as shown in the tutorial). It’s easy to delete any parts one doesn’t want to print. And then everything is just like in the tutorial.
(It’s also possible to select multiple parts and export those, I forget whether that results in the same thing, I believe so.)