Unable to debug C++ from a python script in container

Hello,
I am trying to debug a C++ code from a python script in a dev container, but the breakpoints at my .cpp do not have any effect.
Thank you very much in advance.

Steps to reproduce:

1. Use the following as Dockerfile:

FROM python:3.8-slim

RUN apt-get update &&
apt-get install -y binutils cmake
gcc g++ libtool make
vim curl net-tools unzip procps gdb

2. Use the following as devcontainer.json:
   {
   "name": "Existing Dockerfile",
   "context": "..",
   "dockerFile": "../Dockerfile",
   "extensions": ["ms-python.python", "ms-vscode.cpptools"],
   "runArgs": [ "--cap-add=SYS_PTRACE", "--security-opt", "seccomp=unconfined" ],
   }

3. Use the code myadd.cpp and myscript.py from: https://nadiah.org/2020/03/01/example-debug-mixed-python-c-in-visual-studio-code/

4. Use the following as launch.json:
   {
   "version": "0.2.0",
   "configurations": [
   {
   "name": "Python: Current File",
   "type": "python",
   "request": "launch",
   "program": "${file}",
   "console": "integratedTerminal"
   },
   {
   "name": "(gdb) Attach",
   "type": "cppdbg",
   "request": "attach",
   "program": "/usr/local/bin/python",
   "processId": "${command:pickProcess}",
   "MIMode": "gdb",
   "setupCommands": [
   {
   "description": "Enable pretty-printing for gdb",
   "text": "-enable-pretty-printing",
   }
   ]
   }
   ]
   }

5. Set the appropriate breakpoints in myscript.py (line 5) and in myadd.cpp (line 12)

6. Start Debugging the python script

7. When stop, attach the C++ debugger

8. Continue execution of python script

At this point, a cpptools terminal is created but gdb does not stop in the .cpp code, and the program executes until the end.

Start by reproducing the mixed Python/C++ session using the Dockerfile, devcontainer.json, and launch.json shown in the issue, then inspect the cpptools terminal and GDB attach behavior. Compare breakpoint handling in myscript.py and myadd.cpp; done means the C++ breakpoint is reached after attaching and continuing the Python process.