What steps have you tried?
1, Disable Siri and re-start from System Preferences;
2, Re-open Siri in iCloud;
3, Check sound setting of Mac;
4, Allow Siri and dictation at Scree time setting;
5, Tried safe mode;
6, Recover and reinstall MacOS;
and other actions from google.
the following errors were captured by system console when Siri flashed out.
Error 19:29:12.234065+0800 corespeechd -[CSVoiceTriggerEnabledMonitor _startMonitoringWithQueue:]_block_invoke VoiceTrigger is already OFF, received duplicated notification!
Error 19:29:12.535984+0800 com.apple.preference.speech.remoteservice safelyGetAudioData BTLE could not open audio data file
Error 19:29:12.549462+0800 com.apple.preference.speech.remoteservice PropertyID=1667788144 is NULL
Error 19:29:12.607589+0800 com.apple.preference.speech.remoteservice [C10 IPv6#a7b6e95e.49191 tcp, local: IPv6#b9bf1fd9.53674, prohibit joining] is already cancelled, ignoring cancel
Error 19:29:12.607637+0800 corespeechd [C54 IPv6#6bf94cb9.49192 tcp, local: IPv6#0c512da9.53562, prohibit joining] is already cancelled, ignoring cancel
Error 19:29:12.607759+0800 com.apple.preference.speech.remoteservice [0x60000168b200] Got CANCELED with error [57: Socket is not connected] on reply channel
Error 19:29:12.607866+0800 corespeechd [0x7f9322c0c5f0] Got CANCELED with error [57: Socket is not connected] on reply channel
Error 19:29:12.609036+0800 com.apple.preference.speech.remoteservice [C9 IPv6#a7b6e95e.49191 tcp, local: IPv6#b9bf1fd9.53674, prohibit joining] is already cancelled, ignoring cancel
Error 19:29:12.609070+0800 corespeechd [C53 IPv6#6bf94cb9.49192 tcp, local: IPv6#0c512da9.53562, prohibit joining] is already cancelled, ignoring cancel
Error 19:29:12.609231+0800 com.apple.preference.speech.remoteservice [C10 IPv6#a7b6e95e.49191 tcp, local: IPv6#b9bf1fd9.53674, prohibit joining] is already cancelled, ignoring cancel
Error 19:29:12.609263+0800 corespeechd [C54 IPv6#6bf94cb9.49192 tcp, local: IPv6#0c512da9.53562, prohibit joining] is already cancelled, ignoring cancel
Error 19:29:12.609577+0800 com.apple.preference.speech.remoteservice [C9 IPv6#a7b6e95e.49191 tcp, local: IPv6#b9bf1fd9.53674, prohibit joining] is already cancelled, ignoring cancel
Error 19:29:12.609626+0800 corespeechd [C53 IPv6#6bf94cb9.49192 tcp, local: IPv6#0c512da9.53562, prohibit joining] is already cancelled, ignoring cancel
Error 19:29:12.609709+0800 com.apple.preference.speech.remoteservice [C9 IPv6#a7b6e95e.49191 tcp, local: IPv6#b9bf1fd9.53674, prohibit joining] is already cancelled, ignoring cancel
Error 19:29:12.609766+0800 com.apple.preference.speech.remoteservice -[CSRemoteRecordClient _handleServerEvent:] remoteXPC connection get failed
Error 19:29:12.609837+0800 corespeechd -[CSRemoteControlClient _handleServerEvent:] remoteXPC connection get failed
Error 19:29:12.609946+0800 corespeechd nw_socket_handle_socket_event <private> Socket SO_ERROR [54: Connection reset by peer]
Error 19:29:12.610021+0800 com.apple.preference.speech.remoteservice nw_socket_handle_socket_event <private> Socket SO_ERROR [54: Connection reset by peer]
Error 19:29:12.610063+0800 corespeechd [C53 IPv6#6bf94cb9.49192 tcp, local: IPv6#0c512da9.53562, prohibit joining] is already cancelled, ignoring cancel
Error 19:29:12.610223+0800 com.apple.preference.speech.remoteservice -[VTUITrainingViewController _handleTrainingResultWithStatus:] [VTUITrainingViewController] aborting training because RECORDING_ERROR
Error 19:29:12.610558+0800 com.apple.preference.speech.remoteservice -[SiriUIFlamesAndAuraView setState:] Unexpected mode/state combination
Error 19:29:12.744743+0800 corespeechd -[CSVoiceTriggerEnabledMonitor _startMonitoringWithQueue:]_block_invoke VoiceTrigger is already OFF, received duplicated notification!
Error 19:29:13.347942+0800 SiriUISetupXPC -[ServiceDelegate listener:shouldAcceptNewConnection:] [Setup] XPC connection rejected due to lack of entitlement.