Hey, I think I know which mod you’re talking about https://store.gx.me/mods/sourcen051i5/mikumikumode-/. It looks like it might’ve been removed or hidden from the Opera GX store. Sometimes creators take their mods down for updates, or Opera removes them if they don’t meet certain guidelines. If you still have the mod saved on your device, try exporting or backing it up manually. Otherwise, check the creator’s page or the community to see if anyone has a working version or a reupload. Hopefully, it shows up again soon it’s always annoying when something you like just disappears without notice!