Postcommands not working properly in Github Codespaces

Question

I want to create a codespace for python development with some post commands like: creating a conda environment activate it installing ipkyernel and creating a kernel install requirements.txt

However when I rebuild the container I dont have any error, and when I open the codespace terminal and type conda env list, only thing I see is the base environment

I tried both ways:

1. Put many commands on the same postCreateCommand

    // For format details, see https://aka.ms/devcontainer.json. For config options, see the
    // README at: https://github.com/devcontainers/templates/tree/main/src/python
    {
        "name": "Python 3",
        // Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
        "image": "mcr.microsoft.com/devcontainers/python:0-3.11",
        // Features to add to the dev container. More info: https://containers.dev/features.
        "features": {
            "ghcr.io/devcontainers/features/anaconda:1": {}
        },
        // Use 'forwardPorts' to make a list of ports inside the container available locally.
        // "forwardPorts": [],
        // Use 'postCreateCommand' to run commands after the container is created.
        "postCreateCommand": "conda create --name ForecastingSarimax && conda activate ForecastingSarimax",
        // Configure tool-specific properties.
        "customizations": {
            // Configure properties specific to VS Code.
            "vscode": {
                // Add the IDs of extensions you want installed when the container is created.
                "extensions": [
                    "streetsidesoftware.code-spell-checker"
                ]
            }
        }
        // Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
        // "remoteUser": "root"
    }

2. Or create a .sh script with the commands and execute it

    #!/usr/bin/env bash
    conda create --name ForecastingSarimax 
    conda activate ForecastingSarimax
    conda install pip
    conda install ipykernel
    python -m ipykernel install --user --name ForecastingSarimaxKernel311 — display-name "ForecastingSarimaxKernel311"
    pip3 install --user -r requirements.txt

What am I missing here to have my requirements met? A custom environment with my pip packages and a custom kernel