For the terminal you can set aliases:
Bash users can set the following line in ~/.bashrc
alias code-oss="code-oss --enable-proposed-api ms-python.python"
Or if you prefer to invoke it via the command vscode:
alias vscode="code-oss --enable-proposed-api ms-python.python"
Once that is done run this command to load the conf (or restart).
source ~/.bashrc
If you want to be able to launch it from the system menu instead of the terminal:
cp /usr/share/applications/vscode-oss.desktop ~/.local/share/applications/
Open ~/.local/share/applications/vscode-oss.desktop in an editor and change the line that starts
Exec=code-oss --disable-crash-reporter %U
to
Exec=code-oss --disable-crash-reporter --enable-proposed-api ms-python.python %U
Finally run
sudo update-desktop-database
If you have any pinned / favourites links on your taskbar/panel you will need to remove them and create them again.
Just note this means it will ignore the .desktop file we ship and use your edited version, so if you have any issues with vscode in the future you will have to make sure the files are the same minus your addition.
