Areas you have explored, or even you've been close to will no longer generate new content.

That said, there is a mod that can update these biomes for you, so they DO generate new content. It will try to spare your builds, but of course there's no guarantee that things won't go south, so it is highly encouraged (regardless if you use the mod or not) to make backups of your personal data.

The mod's name is called "UpgradeWorld" and is available through the ThunderStore mod manager, which I can highly recommend.

Mind, you have to run UpgradeWorld only once, then you can disable modding completely.