Unfortunately, you’re also right that the “Container” checkbox only appears when one shape is selected, so you can’t toggle it directly on multiple selected shapes through the UI.
Here are the available workarounds:
Select all the swimlanes you want to modify.
Press Ctrl+E / Cmd+E (or right-click → Edit Style).
In the text box, look for container=1 and delete it (or replace with container=0).
Click Apply.
That instantly “de-containerizes” all selected shapes in one step.
If you already have one swimlane that behaves correctly (Container unchecked):
Select that shape → Ctrl/Cmd + Shift + C (Copy Style).
Select the others → Ctrl/Cmd + Shift + V (Paste Style).
That copies the non-container property too.
The UI hides “Container” for multi-selection to avoid conflicting true/false states, but under the hood it’s just a style flag. Editing the style directly is the same operation that the checkbox performs.
So the short answer:
👉 Yes, you can bulk de-containerize shapes — just select them all and remove container=1 in Edit Style.