Google (and others) change their search algorithms and ranking systems every so often. This is to include new rules, update existing or out of date ones and to reduce the risk of people "gaming the system".

These updates are often quiet small, frequent and go very unnoticed by most people.

Some SEO tools like Rank Math keep an eye on it for you, and alert you in their interface.

Many search engines, like Google, post these updates to the public. You can find Google's on their Search Engine Central Blog.