Can police/hackers unlock iPhones?

iPhone X running iOS 12.3.2 and locked with a 4 digit passcode. iCloud backup, but has been deleted online as well have I changed the Apple ID password. I know that AES 256 bit encryption cannot be decrypted, and I know about the USB Restricted Mode. The phone was past boot phase and had been unlocked once. However, when I lost it, USB Restricted Mode was enabled. Is it, therefore, impossible to brute force it? Because brute forcing such a weak code would be child’s play. Also, would it be possible for a hacker/police to just physically remove the hard drive from the phone, then insert it into some other machine and proceed to brute force? I know about the FBI case with Apple, but that was a while ago. Maybe things have changed? I know the Israelis forensic team and Greykit can unlock up to iOS 12.3. My version is 12.3.2 Also how does Checkm8 fit into all of this?