How do I silence Siri on my HomePod mini?
Try these:
In the Home app on your iOS or iPadOS device, touch and hold a HomePod.
Scroll down, tap the Settings button, then do any of the following:

Deny access to Personal Requests: Tap Personal Requests, then turn off each HomePod you don't want to use Personal Requests on.
Disable “Hey Siri” requests: Turn off Listen for “Hey Siri.”
Disable summoning Siri using HomePod touch controls: Turn off Touch
and Hold for Siri.
Disable indicator light when Siri is listening: Turn off Light When
Using Siri.
Hear a chime when Siri is listening: Turn on Sound When Using Siri.
Turn off VoiceOver: Tap Accessibility to access settings for
VoiceOver and for Touch Accommodations. See Use HomePod touch
controls.

Source: https://support.apple.com/guide/homepod/change-settings-apde6dc8093d/homepod