Could this be uploaded to Modrinth? It is one of the only mods in my pack that isn't on Modrinth so an upload there would be awesome! If a Modrinth release isn't planned, is it okay to distribute your jars in my pack (the actual jar file, not a link)?

No, modrinth is a dying platform at this point.

All good. Is there a reason you believe it's a dying platform? Google trends says modrinth is growing in comparison to curseforge (also keep in mind that curseforge is not only used for Minecraft mods).