It appears that this repository does not have a license. This means that the repository is All Rights Reserved by default, which severely limits what users can do with the mod. In fact, this means that people can't legally use the mod without explicit permission from the author. Also, it also means that people are legally not allowed to fork and contribute to the mod, on account of the license.

For these reasons, I recommend choosing a license that reflects your desires. I recommend the site https://choosealicense.com/ if you're not completely sure on the specifics on each license. LGPL / GPL are generally the best if you want to make sure that other people will contribute their changes back, while keeping the code open source.

While an open source license will prevent you from sending takedowns to mod repost sites, the simple fact of the matter is that most sites are in jurisdictions that ignore US copyright laws anyways. Thus, the choice of a license will not impact repost sites, but it does provide benefits to users and contributors.