How do I know if another device has access to my iCloud information
Someone had my information, can they see what I’m doing on my phone somehow with my iCloud information?? Like spy wear or something ???
If the attackers are any good, you won’t know.
Based on available information, spyware and espionage tooling that installs onto a device is, however, rare, and its use has been targeted.
Tools that install elsewhere and either use your iCloud credentials to access your iCloud, or that installs on a Mac or PC being used for your backups, is somewhat more available.
What to do? Read the following, and run Safety Check as described there:
Personal Safety User Guide - Apple Support
Follow the recommendations there, including enabling two-factor, using unique and robust passwords, etc.
If your devices have been out of your control and/or your passcodes or credentials might have been compromised, then you’ll want to reset those devices and those credentials.
If you think your Apple ID has been compromised - Apple Support