When uploading a mod to Modrinth, we strongly advise against having multiple projects for a single mod. Instead, your mod should be uploaded as one single project with multiple versions supporting multiple mod loaders. You can find projects like this all across Modrinth, such as Cobblemon, Architectury API, or CraftPresence.
Having one singular project has a variety of benefits.
Consolidated downloads will make it easier for people to discover your mod. Since search and discovery is primarily weighted by download count, this leads to more people having the ability to find and use your mod.
Simpler Maintenance, as instead of having to update two project pages and all the work that entails twice, or for each project, every time you update your mod, you only need to do it once.
Multiple Modrinth features take advantage of the fact that projects can support more than one loader. The "Featured versions" panel, for example, will show versions for all available loaders when using the auto-featuring system. The Modrinth App also takes advantage of this by automatically selecting the version that's relevant to a user when they want to add your mod to an instance. Third-party launchers also handle this use case.
These are just a few of the advantages of combining projects and we believe overall it is more convenient for you and for users.