HomePod no longer responds to Siri
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:

Enable “Hey Siri” requests: Turn on Listen for “Hey Siri.”
Enable summoning Siri using HomePod touch controls: Turn on Touch and
Hold for Siri.
Enable indicator light when Siri is listening: Turn on Light When
Using Siri.
Hear a chime when Siri is listening: Turn on Sound When Using Siri.

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