I think someone signed in my iCloud on a browser want me
I think someone’s signed in on my iCloud on a browser
Question marked as
Without revealing apple id account credentials to the person , his device iPhone / ipad / Mac can't be synced with your primary browser Check your Apple ID device list to see where you're signed in - Apple Support
Read Checklist: If you want to see if anyone else has access to your device or accounts - Apple Support
If you think your Apple ID has been compromised - Apple Support