Did you tests the change with opened workspace?
Because it breaks my current configuration:

{
            "name": "test_app",
            "request": "launch",
            "type": "dart",
            "program": "lib/main.dart",
            "flutterMode": "debug",
            "args": [
                "-d",
                "chrome",
            ],
}

If i remove the program it runs perfectly now.

@maik-kluwe can you provide more details about your exact setup? What do you mean by "opened workspace"? Do you mean a .code-workspace file? If so, is this launch configuration inside the .code-workspace or inside .vscode/launch.json inside one of the workspace folders?

If the config above is inside the .code-workspace file then it is expected that this will fail. The issue is that relative paths in files at the workspace level are ambiguous, for example:

{
	"folders": [{
			"path": "/Users/danny/Desktop/dart_sample"
		}, {
			"path": "/Users/danny/Desktop/dart_sample_2"
	}],
	"launch": {
		"version": "0.2.0",
		"configurations": [
			{
				"name": "Dart",
				"type": "dart",
				"request": "launch",
				"program": "bin/main.dart" // Is this path relatve to dart_sample or dart_sample_2 ?
			}
		]
	}
}

Although this worked before, it was using the current open file which is not guaranteed to be correct (if you opened a file from another workspace folder and pressed Run, it will behave differently, and it's not clear that was expected).

If you have launch configurations with relative paths in the workspace file, you should use variables to indicate which workspace folder they are relative to:

https://code.visualstudio.com/docs/editor/variables-reference#_variables-scoped-per-workspace-folder

For example:

{
	"folders": [{
			"path": "/Users/danny/Desktop/dart_sample"
		}, {
			"path": "/Users/danny/Desktop/dart_sample_2"
	}],
	"launch": {
		"version": "0.2.0",
		"configurations": [
			{
				"name": "Dart",
				"type": "dart",
				"request": "launch",
				"program": "bin/main.dart",
				"cwd": "${workspaceFolder:dart_sample_2}", // This uses the workspaceFolder path from dart_sample_2
			}
		]
	}
}

If you want it to run "whichever project the open file is in" then you should be able to use ${fileWorkspaceFolder} or ${workspaceFolder}.

If this isn't the issue you are seeing, please file a new issue and include specific details that will help me reproduce. Thanks!

Sorry about the missing information.

In my case i have created a .code-workspace file with just the name and paths of the projects in it:

{
	"folders": [
		{
			"path": "C:\\path_to_project\\project1"
		},
		{
			"path": "C:\\path_to_project\\project2"
		},
		{
			"path": "C:\\path_to_project\\some_package"
		}
	]
}

In each of the Projects (in my case project1 and project2) there is an .vscode\launch.json config with the configuration posted earlier.

My assumption was that with this setup dart should know the location of the cwd / currentWorkingDirectiory.

At the end:
@DanTup your tip with variables to indicate which workspace folder has helped. I was missing the "cwd": "${workspaceFolder}", in my launch.json. Now it works like before. Thanks!

@maik-kluwe you are correct - if the launch config is inside the project folder, this should work - I'll take a look shortly. Thanks!

I can repro this - have opened #4239 and will do some digging. Sorry for the bother!

@maik-kluwe can you switch to the pre-release (v3.53.20221102) Dart extension and verify it fixes your problem? If so I'll push it out to the stable version:

It works 👍 Thank you!

Great, thanks for confirming! I'll push it out to stable shortly.