This is a built-in behavior that selects the most similar words, just the menu with sentences is not always shown. In Linux, the offer menu can be shown explicitly by pressing Alt + / , or you can try the "add-on blindly" by pressing Tab until the desired option appears. Hotkeys can be found by looking for auto_complete
in the file with "Key Bindings - Default" (available in the command palette).

As far as I understand this system, it works in tandem with syntax highlighting and uses its scopes to understand whether autocomplete is appropriate . You can separately specify in the settings the selector, which is considered appropriate . Let's say this one will cover all selectors starting with source
(source code) and text
(plain text), that is, almost everything :
"auto_complete_selector": "source, text"
... add to the file with user settings. And in order to calculate the necessary scopes, you can install ScopeHunter and see its output in the places of interest.