Warning: Poco F3 is different from the Poco F3 GT available in some regions - GT uses Mediatek Dimensity 1200 instead of Snapdragon 870. Mediatek SoCs don't work well with LineageOS.
2 things that make me much less excited about how much control I have:
There is still a xiaomi boot rom running under Havoc or Lineage, I can only assume xiaomi can put anything they want in that, so my phone isn't more secure, it's just less bloated.
Also, once you unlock you can now get access to the phone with a computer, bypassing the password. It becomes physically less secure. I believe there are some full storage encryption options but they seemed very finicky.
Please correct me if I'm wrong with any of the terminology, I last messed with this months ago. Sad that these are our options (walled garden and/or wiretap ourselves).
Just set up encryption. Once it works, it works, so it's worth it.