Encrypting custom ROM I'd like to encrypt my phone, but I'm afraid it might interfere with the Over-The-Air updates of the custom ROM I installed via flashed TWRP. Does the custom ROM need to support encryption somehow? Is this generally considered seamless or problematic?

Also I am not sure how does the encryption go along with rooted phone. Why do I need to unroot the phone for the encryption process?
Go ahead and encrypt your phone. TWRP can decrypt and flash ROMs when given the password. I personally​ use a custom ROM (LineageOS 14.1) and have encryption enabled.