How Do I Apply to Become a Marketplace Creator?
Solution 1:
You must be part of the Minecraft Partner Program. On this page, you can apply.
Keep in mind that demand to be a partner is very high; it is common to have to wait several months to even hear a reply. You also must show that you have the skills to create content, such as a portfolio of existing creations (worlds, skins, etc.) that you have personally created.