If you are seeing a "Too Exposed" message in Valheim when using the Fermenter, it doesn't mean that there's anything wrong with the Fermenter itself, the issue is easy to fix. Once resolved, you can use the fermenter to convert base meads into useful potions for battling enemies in various biomes.
Here is what the "Too Exposed" message means, and how to fix it.
Valheim Fermenter Too Exposed: What Does it Mean?
When you see the "Too Exposed" indicator pop up while trying to use the Fermentor, it means that your Fermentor is exposed to the sky, and doesn't have a proper roof.
To fix this, make sure that whatever shelter you put the Fermentor inside has a structure explicitly labeled "roof" over it. Just a wood floor as a roof will not be enough to fix it. Craft and place a roof over your living structure with the Fermentor inside to give the Fermentor less exposure and proper space to work.
Once you fix this roof-issue, it will take two or three in-game days to brew and convert your mead-base into mead.