I want to cancel my Apple account.

If you really want to delete your Apple ID account, and not just sign out of it, see→How to delete your Apple ID account - Apple Support

Read the link CAREFULLY; deleting an account is permanent, and can have serious consequences, including making all of your Apple devices permanently unusable. So be sure to sign out of Find My on all devices before doing it; any that are not signed out will be locked and unusable forever.

For emphasis this is from that article:

• When your Apple ID account is deleted, your account details and the data associated with your Apple ID are permanently deleted from Apple’s servers. You can't sign in to your account, and you won’t be able to access any data, content, or services that were associated with your Apple ID.
• Photos, videos, documents, and other content that you stored in iCloud are permanently deleted; you can't receive any messages or calls sent to your account via iMessage, FaceTime, or iCloud Mail; and you can't sign in to or use services such as iCloud, the App Store, iTunes Store, Apple Books, Apple Pay, iMessage, FaceTime, and Find My iPhone. In addition, any Apple Store appointments and AppleCare support cases are canceled.
• Deleting your Apple ID is permanent. After your account is deleted, Apple can't reopen or reactivate your account or restore your data. If you aren’t planning to use your account for now but may consider returning to it in the future, we recommend temporarily deactivating your account (where available) instead of deleting it.

Just sign out.