Google announced the December 2022 link spam update on December 14, 2022 in a Search Central blog post, estimating about two weeks to roll out. It actually took 29 days, completing on January 12, 2023, the same day as the December 2022 helpful content update that had been rolling out alongside it. Google's Danny Sullivan explained the delay: "Rollouts can slow or pause when we get into the holiday periods."
It was the first link spam update to lean on SpamBrain, Google's AI-based spam prevention system, for links: Google said SpamBrain can "detect both sites buying links, and sites used for the purpose of passing outgoing links". The update applied to all languages, and Google warned that rankings may change as spammy links are neutralized and "any credit passed by these unnatural links are lost". In other words, links gained through spam were devalued at scale, not just ignored.
Because neutralization removes benefit rather than imposing a penalty, a drop during this window most likely meant a site had been gaining from unnatural links, and there was no manual action to lift. Google's advice was to focus on producing high quality content and improving user experience rather than chasing links, and to make sure affiliate or paid links are properly qualified.