Stop any syncing with other apple devices with same Apple ID and MacBook
Syncing happens in the system settings, iCloud. If you sign out there, you stop syncing. 


https://support.apple.com/en-us/HT208242


You can stay signed in to the App Store and not sign in to iCloud as well, just skip the full setup when you set up your account - choose set up later if you are asked if you want to sync iCloud.