How to fix suspicious Text-to-Speech Messages on Mac?

There are all kinds of non-nefarious things this could be.

The first that comes to mind is the built-in Accessibility support for blind or visually-impaired users - specifically the ability to 'read' what's on the screen - this sounds like an incoming message that the OS is 'reading' to you.

The OS has this ability built in, and can read from any application - check System Settings -> Accessibility -> Spoken Content to see which (if any) options are enabled.

Discord also has its own built-in trigger to read incoming messages to you. Check Discord settings -> Accessibility -> Text-to-Speech to see if it's enabled there.

The other, even simpler, option is that someone sent an audio file through Discord and that's what you're hearing.

Beyond that, there's no malware that I'm aware of that will arbitrarily speak content to you

If there is Malware installed on this computer

It would be because the user ( you ) was duped into installing this Malware

Then perhaps, unknowing, the user chose to By-Pass the Builtin Security Apple has to protect against Malware by giving Permission to install

Protecting against malware in macOS

Download the Trusted Application Etrecheck ( External Link ) directly from the Developer

It can catch Malware and possible remove it