Yep, there is a creative mode.

You need to add the "-console" command into the launch options for Valheim in Steam.

Then once you load into your save, hit F5, type in "devcommands" hit enter, then "debugmode" and hit enter again.

Escape to get out of the console, then hit "B" to turn on endless resources with the hammer (and everything else in the workbench/TAB menu). In this mode, you can repair without being at a workbench too.

Enjoy building with ALL OF THE THINGS.

Be careful, there are loads of things you can spawn into your game using the console, some of these are game-destroying. If you just want a free-build mode, just follow the above and enjoy.

As already mentioned, definitely back your save up because you WILL try to do something stupid. Most of us who venture into the creative mode do and it sucks when you ruin or break a favourite. I highly recommend creating a "try anything" save where you can see what heppens before you try anything in your main.

Have fun!