iCloud keeps popping up with old Apple ID

Since the last time this question was asked appears to be almost 10 years ago, I don't think the previous solutions may be applicable anymore. Anyhow, I recently got my first iPhone, an iPhone 14, and I'm trying to integrate it with my established tech, some of which is quite old. I have a Dell laptop running Windows 10 with iTunes on it, which had an old Apple ID with an email address I no longer use. I have (I thought) updated my Apple ID and password with Apple, but iTunes still shows the old one. More annoyingly, I am now getting constant (like every minute, no exaggeration) pop-ups from iCloud telling me to enter my password to proceed but the old Apple ID is preloaded and I cannot update it on that pop-up. As if that wasn't enough, there is a secondary pop-up saying that the version of Outlook I have is not supported, but I don't even have Outlook, I have the generic version of Mail that came with Windows 10. Help.