How can I delete Time Machine without a password?

+1 to @rkaufmann's post regarding using a password manager.

I've found Apple's new Passwords app to be very easy to use. It provides for password management as well as passkeys, codes, and wi-fi passwords among other things. It seems to be well integrated with the macOS and leverages the security of TouchID so its access is protected. It syncs across devices by means of the Apple Account. And it's already installed on the Mac with macOS.

Use the Passwords app to create, manage, and share passwords and passkeys across Apple devices - Apple Support

Hi,

Try to reformat your TimeMachine drive with DiskUtility, then use it as TimeMachine drive.

You probably need to get yourself a password manager. Chances are you are like most of us and have a LOT of logins and passwords to keep track of. There are tools such as 1Password that just that. 1Passwords s just one example, there are others so please look in the Mac App Store for Password Managers and perhaps you will find one that suits your needs.