Multiple mods dont really work because they require mods that arent on aternos. For an example here: "https://www.curseforge.com/minecraft/mc-mods/wizards" Wizards [Fabric] needs:
GeckoLib (Already is on aternos)
Spell engine also needs:
Spell Power Attributes (Others on this list are already on aternos, but spell power attributes isnt on aternos.)
Hopefully these fixes will be done to other mods aswell, im not aware of many others but this is just an example.