I think it was whenever they stopped giving the Moto G series numbers (G5, G7, etc), and just started making them "Moto G (Year)". Official LineageOS support has gotten worse since then, but I don't know if it's because they can't find maintainers or what.
I diverted recently, but I used budget Moto G's for a decade and couldn't have been happier with the stock OS.
Maybe they finally succombed in 2024.