As far as I know, the mistlands biome already existed before this update, but it was essentially empty misty terrain. Regions of that biome that you already explored will continue empty (although with changed elevation, so if you built there chances are your stuff will be buried underground), but if you haven't encountered that biome before then it'll be populated with the new content without having to start a new world once you find it.

if you have explored most or all of your map, yes, you must create a new world, they can't regenerate generated terrain, so if you only explored a few islands near the centre of the map you can use that world just fine, but if you explored most of the middle band and a good deal of the north and south, you need to make a new world.

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!

I started my server and it put me in the cirlce stones and all my previous work , lodges, bases and exploration was gone. WTF. i didnt start a new game , so the update wiped my server.

Originally posted by Thorshammer:

I started my server and it put me in the cirlce stones and all my previous work , lodges, bases and exploration was gone. WTF. i didnt start a new game , so the update wiped my server.

Thats something you will have to ask your server provider (or if you have your own handy, you will have to debug it)

yes the Mistlands update. thanks for the reply.

Originally posted by Julius_213:

must i creat a new world for use the mistlands content ?

Absolutely not. I don't know why people keep re-asking this.

i knew that you didnt have too restart a new map , but it somehow deleted all my progress in the update. I will send request too server provider to see if they can recover my explored areas and bases and docks etc.

Also a question i would like answered. I have two main saves one has almost nothing uncovered and was made just before home and hearth and one that has a lot uncovered and was made when the game first went into early access.
I think its recommended but not necessary, but what that really means and if it will cause problems i dont know. I don't think I can sum up the interest to start all over again, even if i use my main character and haul all the decent materials into a new world.

From the patchnotes it seems like you dont NEED to unless you discovered basicaly every bit of the map as mistlands appear in unexplored areas. But thats just my guess from patchnotes