In my experience as a moderator for Modrinth, one of the most common rejection reasons is invalid metadata. Most commonly it relates to licensing, where they will select one license on Modrinth but still have the default CC0-1.0 license in their LICENSE file and in the fabric.mod.json.

If this template generator is going to eventually become the recommended way of creating a new mod, the one improvement I would like to see the most is to not assume that everyone is going to use CC0. Instead, the user should be prompted to select their own license, like how the MinecraftDev plugin does it:

Or how Modrinth does it:

Ideally there would also be a link to one of the many useful guides for choosing a license, such as GitHub's choosealicense.com or Modrinth's licensing guide.