A police department can’t break into anything. They either use 3rd-party tools made by companies like Cellebrite or MSAB, or they send a device to e.g. the FBI (who might sometimes have custom tools, but most of the time they also just use some tool made by some forensics company like Cellebrite). The only reason why forensics companies don’t offer SailfishOS exploits, is because it’s way too obscure, and developing an exploit wouldn’t be profitable by any means. That doesn’t mean that SailfishOS is exploit-proof though. Defending against brute-force attacks requires a hardware secure element, like the Titan M2 or Apple Secure Enclave. Jolla phones simply don’t have secure elements.

GrapheneOS is the only OS that’s “Cellebrite-proof”, as can be seen in leaked internal docs from Cellebrite.

SailfishOS is also paid and mostly proprietary. There’s no reason to trust it more than proprietary Android or iOS. In fact, I’d prefer a modern iPhone (12 or later) with the Apple Secure Enclave over a equally proprietary, but less secure device that lacks a secure element. The UX is also a million times better. And yes, I have tried SailfishOS in the past, back when it only ran on Sony Xperia phones. It even was my daily driver for a couple of months.