Often you'll see these posts that are like:
"bad cringe ugly dms: nooooooo you can't homebrew an axe, it breaks immersion! Also, no extra races!"
"cool based totally rad dms: a flamethrower? Nice. A half werewolf half aaracocra? Sure."
I don't like this mentality. Sure, infringing on the players' creativity can ruin the game for them, but that doesn't mean you shouldn't have your own boundaries. Sometimes you're not experienced enough to confidently dm something, or you just don't want to deviate from your setting. The DM is , among other things, a storyteller, and they have to keep things together in such a way that the story is cohesive. If your players can't make creative characters that they enjoy while working within the limitations of your game, well that's really a skill issue, isn't it? You should encourage them to research more, or find ways to make interesting builds that fit your setting.
Again, be careful not to become the fun police, but if something doesn't match the story that you wanna tell, let your players know that. They may be the protagonists, but you are the narrator, and you should get a say in things.