The top image is VS Code's builtin Monokai dimmed theme which correctly colors the typescript return type tokens. The bottom image is one of these themes (they all fail to color correctly).
A clearer difference might be between the VSCode built in Monokai (top) vs this extension's Monokai Classic (bottom):
Looks to be related to https://github.com/Monokai/monokai-pro-vscode/issues/148
The top image is VS Code's builtin Monokai dimmed theme which correctly colors the typescript return type tokens. The bottom image is one of these themes (they all fail to color correctly).
A clearer difference might be between the VSCode built in Monokai (top) vs this extension's Monokai Classic (bottom):