Hello. Although the sound and vibration is on when called, there is no sound on the venu 3.
You'll want to ensure Tone setting is enabled for Calls on the watch: Menu > Settings > Notifications & Alerts > Smart notifications > General Use > Calls > Tone.
You'll also want to ensure Call Audio is enabled: Menu > Settings > System > Connectivity > Phone > Call Audio.
If you Continue to experience this, please reach out to your local Garmin Support team.