As an Evangelist for one Mod that ought to be part of the Base game, and I know I know "Mods not officially supported bl bla blah" But the answer to all these sort of threads remains:
https://www.nexusmods.com/valheim/mods/1485?tab=description

Upgrade world a Mod you can use ONE TIME and update an old world to the new content then uninstall if you wish. I use it regularly works every time, even if you wanna refresh things like mined out Caves in the mountains or some such.

Many of us especially ME have become attached to our exciting worlds I know. While Valheim is in EA a feature like this ought to be included either in the base game or as an official tool to refresh after updates with any substance to them!

But until they come to their senses the Mod community like the author of the above is fixing the obvious mistakes like this!