WhatsApp messages cannot be transferred to computer if the ‘End-to-End Encrypted Backup’ option is turned on.
When this option is enabled, the messages are securely encrypted and stored on the device, and Tansee does not have access to them.

1. Open WhatsApp on your iPhone and go to Settings - Chats - Chat Backup.
2. Tap ‘End-to-End Encrypted Backup’.
3. Tap Turn off, then enter your password or 64-digit encryption key.
4. Tap turn off again to confirm.

Please download and install the latest version of Tansee iPhone Message Transfer here.
Additionally, to access iPhone messages, you will need to install the Apple Mobile Device Support component 64-bit or 32-bit.

Another option: 'Apple Mobile Device Support' component is included in iTunes. Click here to download and install the latest version of iTunes and verify that it is able to read your iPhone, iPad or iPod Touch.
What to Do If iTunes does not recognize my iPhone?
What to Do if iTunes can not be installed or uninstalled?

What to Do If Tansee iPhone Message Transfer Does Not Recognize My iPhone?

If you have a large number of apps or photos, Tansee will take longer time reading data.
What to Do If Tansee iPhone Message Transfer Keeps Reading Data?
If asked, unlock your iOS or iPadOS device using your passcode. If you see a prompt on your iOS or iPadOS device asking you to Trust This Computer, tap Trust to continue.

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How to Uncheck iTunes Backup Password?
How to Reset iTunes Encrypted Backup Password?

And then click the button labeled 'Save' located at the bottom of the screen.
Choose to save all your iPhone, iPad, or iPod messages to your PC in ANTS, HTML, TEXT, PDF or JPG format.
By selecting save to .ANTS format, you can backup all messages from iPhone or iPad to computer, and also set a password to protect your SMS, MMS and iMessages database for personal privacy.
Select the desired contact from the Tansee contact list, and then click 'Save.'
Select the messages by date and then click 'Save'.