Can police/hackers unlock iPhones?
There isn’t a hard drive in iPhones, and Apple has engineered things so that it’s very expensive to get to the leads and snoop or alter the electrical signals to defeat encryption, so there’s no trivial path to decrypt or bring another os to your storage. 

However, you should assume that unless you’re very good the police and government can get your data by coercion or brute force - especially if their budget is $25,000 or more (and maybe far less to compromise some devices). Your 4 digit pass phrase is the weakest link so that weakens your protection substantially if iOS is not set to self erase after 10 failed attempts. 

Also, just because an exploit or jailbreak isn’t out now, doesn’t mean they can’t image or keep your device and crack it later. The iPhone X is way on the “more secure” side so unless you chose a weak pass phrase, you’re probably safe for some time to come if they didn’t get your data from a subpoena / home computer which are far easier to seize and crack and then get to your records by account takeover. 

There are jailbreaks for your device on both iOS 12 and iOS 13 so I wouldn’t assume you’re safe if they have physical control of the device and time to work it and get USB active:


https://www.reddit.com/r/jailbreak/wiki/escapeplan/guides/jailbreakcharts
https://www.reddit.com/r/jailbreak/comments/czkyje/meta_latest_jailbreak_release/