Unknown device added to iCloud account
Earlier today I noticed in my iCloud settings on my iPhone 15 Pro that a new device had appeared - a MacBook Pro which I did not recognise.
I immediately removed the device from my account, changed my iCloud password, passwords to banking apps, email account associated with banking etc - and I'm pretty satisfied that my account is secure. I will of course continue to monitor (as I always do) for any odd activity. There has been no suspicious activity on my account at all.
I don't understand how this can have happened. I have 2FA enabled everywhere, and any new device would have to be approved through Apple's own 2FA by verification on my iPhone or MacBook. My iCloud account has a very secure (20 character) password which is not stored anywhere online and which no one else knows.
Does anyone here have any ideas, please?
Thank you!
iPhone 15 Pro