Call waiting service is not working in my iPhone 13 Pro max

SMS, MMS, WiFi calls, Call Forwarding, Call Waiting, Call Merge, Conference Calls, hotspots, and Voice Mail (Visual or Normal) all are Carrier Specific features. Contact your Carrier (Cellular Service Provider), the agency that issued the SIM / eSIM to you.

The Hotspot is a Carrier Specific feature. Contact your Carrier (Cellular Service Provider), the agency that issued the SIM / eSIM to you.

VoiceMail is a Carrier Specific feature. Contact your Carrier (Cellular Service Provider), the agency that issued the SIM / eSIM to you. Voicemail, Visual Voicemail, and Voicemail transcription are available from select carriers in select countries or regions.

WiFi Call is a Carrier Specific feature. Contact your Carrier (Cellular Service Provider), the agency that issued the SIM / eSIM to you.

You want to call your carrier for issues regarding call waiting. It also looks like you have Dual SIM with the second line being inactive, so that may be causing issues as well.