Does Quark officially support Fabric?
Official Quark distribution currently lists Forge and NeoForge as supported platforms, with the active Minecraft 1.21.1 line using NeoForge. There is no official Fabric build to install alongside Fabric Loader.
If your existing pack is Fabric-only, Quark itself is not a drop-in option. Do not rename files, change extensions or use random “converted” downloads in an attempt to bypass the loader requirement.
Why loader mismatch causes startup errors
A mod is compiled against loader-specific APIs and metadata. NeoForge and Fabric discover mods differently and expose different interfaces, so a NeoForge mod in a Fabric mods folder is rejected or ignored.
The same idea applies to dependencies. Modern Quark versions use Zeta, and that dependency must match the same Minecraft and loader environment.
What to use for Minecraft 1.21.1
For Quark 1.21.1, build your profile around NeoForge and a compatible Zeta version. Keep the game version, loader, Quark and dependency as one matched set.
If a server uses Quark, confirm the server pack’s exact versions instead of assuming that any 1.21.1 Quark file will work.
How to avoid unsafe “Fabric ports”
Do not trust an unfamiliar download simply because its title contains “Quark Fabric.” Check whether a project is official, whether the author and license are clear, and whether the file is intended for your loader.
An unofficial project may be a different mod with similar goals rather than a true port. Treat it as separate software and assess it on its own merits.