It means modpack is build on specific Mod Loader - Forge, Fabric, Quild, Paper(and more i dont heard of) Afaik MyM is using Forge bc they have self-written plugins that works on Forge only and sadly are very outdated thats why we dont get any 1.16+ modpacks open to public but patrons(beside long forgotten vanilla). Its about having MyM plugins to do MyM stuff like patrons, legacy tiers etc. on servers they host or not, and they prefer to provide full of their services to people who literally pays for running the network. So summarizing - @Fabreazi I dont think we get any fabric modpack anytime soon.
