How to disable voicemail on iPhone 12 Pro Max

Please contact your Carrier for enabling or disabling VM as VoiceMail is a carrier-specific feature --> Check your voicemail on iPhone - Apple Support

VoiceMail, whether it's visual voicemail or the traditional voicemail service, is a carrier-specific feature that depends on your cellular service provider. If you are experiencing any issues related to voicemail on your iPhone, it's essential to get in touch with your carrier for assistance.

Bichala wrote:

I am not facing any problems in voicemail it is just that I want to disable voicemail completely on my device.

Only your carrier can remove it. Contact them.