in code-server console
<code>
git clone https://github.com/flutter/flutter.git -b stable --depth 1 /config/flutter
export PATH="/config/flutter/bin:${PATH}"
export ANDROID_SDK_ROOT="/config/android_sdk"
export PATH="$PATH:$ANDROID_SDK_ROOT/cmdline-tools/latest/bin:$ANDROID_SDK_ROOT/platform-tools"

sudo apt-get install unzip
flutter doctor

don't do this...
sudo apt update && sudo apt install android-sdk
installed in /usr/lib/android-sdk
sudo apt remove android-sdk
sudo apt autoremove

unzip the command line tools
./cmdline-tools/ ./latest && mkdir cmdline-tools && mv ./latest/ ./cmdline-tools/latest/

sdkmanager "build-tools;34.0.0" "platforms;android-34" "platform-tools"

PATH="/usr/lib/android-sdk/cmdline-tools/bin:${PATH}"

</code>