The delay mostly came from Google, not from the LineageOS team. Around the launch of Android 16, Google stopped publishing the device trees and driver binaries for its Pixel phones. Those files tell a custom ROM how to talk to a specific phone’s hardware, such as its camera, modem and fingerprint sensor.
Without them, volunteers have to rebuild that knowledge on their own, which is slow and fiddly. Delays to Google’s public kernel downloads for Pixel devices made the job harder still. The kernel is the core layer of the operating system that sits between apps and the hardware.
The same change has slowed other privacy-focused projects that build on Pixel hardware, which is why Pixels, once the easiest phones to modify, have become a tougher target. The good news is that Pixel 10 builds landed on the same day LineageOS 24 was announced, rather than months behind it.