If Siri isn’t responding to you, go to Settings > Apple Intelligence and Siri > Talk and Type to Siri > Turn it Off then back on to either “Siri” or “Hey Siri” and “Siri”. You will be asked to read a set of verbal prompts which will help Siri better recognize and understand your voice to respond.
If Siri isn’t speaking aloud, go to Settings > Apple Intelligence and Siri > Siri Responses > Prefer Spoken Responses.
Otherwise, please specify.