Not sure if this is an issue with the Playdate extension for Nova or pdc but it seems like you can't set a breakpoint if the Lua file is located outside the Source folder.
I get this in Nova:
Request “setBreakpoints” failed: requestFailed(Optional("Missing required argument: Could not resolve file path: /Users/didier/Documents/Code/Playdate/PokeCrossing/toyboxes/DidierMalenfant/pdutility/tiled.lua"), nil)
I suppose files outside the source folder are ignored by pdc, so you can't debug that file because it never gets transferred to your playdate
I thought about that too but pdc does parse any import statement found in your Lua files so those files actually do make it across. I can execute code in them, just not set breakpoints.