I have 2 monitors connected to my mac mini

Try Audio MIDI Setup (Utilities folder in Applications). In its Help menu, click the triangle next to "Set up audio input and output devices", and select "Play audio through multiple devices at once".

What year model Mac Mini?

What monitors and how are they connected to the Mac Mini?

Try this, go to Applications > Utilities > open the Audio MIDI Setup and see if you can configure a setup that combines the speakers in both external displays. see > https://www.macobserver.com/tmo/article/audio-midi-setup-your-macs-secret-sound-manager