What are the mods? Sodium is a free and open-source rendering optimization mod for Minecraft 1.16+ which greatly improves frame rates and stuttering while fixing many graphical issues. While Iris is an open source shaders mod. Both rather well-known for Minecraft fans.
What's going on? Well, according to the official Twitter account for Iris, they explained they were having technical issues with CurseForge along with difficulty in actually uploading anything. Apparently the newer CurseForge is quite broken and according to the Iris team CurseForge are "prioritizing modpacks that rip off out mod's branding in search results" and their revenue from CurseForge has been declining "despite the fact that the number of downloads has been increasing month-over-month". In a later Twitter post, the Iris team mentioned that "Effective immediately, Iris and Sodium have been pulled by Overwolf for encouraging users to download from Modrinth and archiving files. Modpacks will be broken.".
So now they're recommending all users move over to Modrinth, an open source mod hosting platform, that works directly with many popular Minecraft launchers like Prism that work great. Here's a shot I took with Iris, Sodium and Complementary Shaders v4:
Seems like a messy situation, hopefully the move to Modrinth will go well. Modrinth overall seems like a good platform for Minecraft modding, putting the power more in the hands of everyone.