Work on one panel alone, or carry it to another device.
A manga page is big, and one panel on it is small. The Workbench takes one panel off the page and lets you work on it alone, filling the window. When you are done you put it back.
Choose the frame tool, the last one in the strip, and click inside the panel. The panel is selected, and Open in Workbench appears at the top of the right side. Press it.
The panel opens by itself. The tools are the same; the layer list shows only this panel's layers. Anything on a layer outside the panel, such as lettering that sits over the whole page, stays behind on the page.
The back arrow asks which of the two you want, so you cannot leave by accident.
While a panel is in the Workbench, it is locked on the page: you cannot draw on it there, so the two never disagree.
Lay out a page on your Mac, then ink one panel with Apple Pencil on your iPad. Continue Elsewhere carries that panel over iCloud; Send Back brings your edits home. You can go from iPad to Mac, too.
Here is the journey, illustrated. One panel travels; the rest of the page stays where it is. The three pictures are drawings of the idea, not the app's screen: the buttons are where the steps say.
Select the panel with the frame tool, then press Continue Elsewhere, below Open in Workbench. Wait for Sent — ready on your other device.
Open MangaLoft on your iPad. When the waiting part appears, tap Open. The panel opens by itself in the Workbench, ready to draw on.
When you are done, choose Send Back on the iPad. Then open the original page on your Mac. The returned edits are applied automatically.