I've no idea if this is an issue with MultiMC/Fabric/Mod, but i get the following error when i try to launch my client:
Error:

• Incompatible mod set!
  net.fabricmc.loader.impl.FormattedException: Mod resolution encountered an incompatible mod set!
  A potential solution has been determined:
• Install fabric, any version.
  Unmet dependency listing:
• Mod 'Nicephore' (nicephore) fabric-1.19.x-1.0.0 requires any version of fabric, which is missing!
  at net.fabricmc.loader.impl.FabricLoaderImpl.load(FabricLoaderImpl.java:190)
  at net.fabricmc.loader.impl.launch.knot.Knot.init(Knot.java:148)
  at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:68)
  at net.fabricmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:23)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
  at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.base/java.lang.reflect.Method.invoke(Method.java:568)
  at org.multimc.onesix.OneSixLauncher.launchWithMainClass(OneSixLauncher.java:210)
  at org.multimc.onesix.OneSixLauncher.launch(OneSixLauncher.java:245)
  at org.multimc.EntryPoint.listen(EntryPoint.java:143)
  at org.multimc.EntryPoint.main(EntryPoint.java:34)

You need to install the Fabric API mod, which is a mod you install on top of Fabric.

I just came across Fabric API, decided to check if this issue has been resolved, and yep, that's what i was missing..