Both the native Windows and macOS apps have spell check and settings are controlled at the OS level. If you are using the web client, your browser settings control the auto-correct options.
On Windows, you can enable and disable at a system level via the
On macOS you can set the behavior at the OS in
System Preferences >
Text tab or by right clicking in a chat thread and choose the
Spelling and Grammar setting which will override the system setting for Amazon Chime.