How do I stop syncing my Apple Account?

You can select which features you wish to sync. Read these support articles, the first one appears to directly address your issue:

Change which apps sync and store data with iCloud - Apple Support - "'When you turn off an iCloud feature on a device, information stored only in iCloud for that feature is no longer available on the device. If you turn off Mail, Contacts, Calendars, Notes, Reminders, or iCloud Photos on just one device, you can still view and change your information on iCloud.com and on another device you set up for that feature."

Set up iCloud on your iPhone, iPad, or iPod touch

Sign in to iCloud on all your devices - Apple Support - Set up iCloud on all your devices - Apple Support

Change iCloud preferences for your Apple ID on Mac --> Change iCloud settings on Mac - Apple Support

Do you want to stop using your Apple Account?

If yes, have a look at the related articles about deleting your Apple account temporarily or permanently by clicking on the blue linked article:

How to deactivate your Apple Account - Apple Support

How to delete your Apple Account - Apple Support

Before you start, make sure to save your iCloud data first:

Archive or make copies of the information you store in iCloud - Apple Support