Hello,
you might have heard of a new site called Modrinth, its a new open source website for hosting Minecraft mods (mainly fabric mods).
a lot of fabric developers have been moving over to Modrinth and to be there exclusively even Jellysquid the original creator of Lithium, phosphor and sodium said that all their mods will eventually be Modrinth exclusive and since Aternos doesnt support downloading mods from Modrinth it feels like the Fabric modding community is pushed to the side in favor of Forge.
So im hoping the Aternos team is looking in to adding Modrinth support soon or in the future.