What happened?

Incompatible mods found!
net.fabricmc.loader.impl.FormattedException: Some of your mods are incompatible with the game or each other!
A potential solution has been determined, this may resolve your problem:
- Replace mod 'Better End' (betterend) 21.0.2 with any version that is compatible with:
- bclib, any version
- bclib, any version
- Replace mod 'BCLib' (bclib) 3.30.1 with any version that is compatible with:
- minecraft 1.21
More details:
- Mod 'BCLib' (bclib) 3.30.1 requires version 1.20.3 or version 1.20.4 of 'Minecraft' (minecraft), but only the wrong version is present: 1.21!
- Mod 'WunderLib' (wunderlib) 1.30.0 requires version 1.20.3 or version 1.20.4 of 'Minecraft' (minecraft), but only the wrong version is present: 1.21!
- Mod 'Better End' (betterend) 21.0.2 requires version 21.0.5 of mod 'BCLib' (bclib), but only the wrong version is present: 3.30.1!
- Mod 'Better End' (betterend) 21.0.2 requires any 21.0.x version of wover, which is missing!
- Mod 'Better End' (betterend) 21.0.2 requires any 21.0.x version of mod 'WunderLib' (wunderlib), but only the wrong version is present: 1.30.0!
- Mod 'Better End' (betterend) 21.0.2 is incompatible with any version before 21.0.5 of mod 'BCLib' (bclib), but a matching version is present: 3.30.1!
- Mod 'Better End' (betterend) 21.0.2 is incompatible with any version before 21.0.3 of mod 'WunderLib' (wunderlib), but a matching version is present: 1.30.0!
at net.fabricmc.loader.impl.FormattedException.ofLocalized(FormattedException.java:51)
at net.fabricmc.loader.impl.FabricLoaderImpl.load(FabricLoaderImpl.java:195)
at net.fabricmc.loader.impl.launch.knot.Knot.init(Knot.java:146)
at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:68)
at net.fabricmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:23)

BetterEnd

1.21

BCLib

1.21

Fabric API

1.21

Fabric Loader

1.21

Minecraft

1.20.4

Relevant log output

No response

Other Mods

No response

As the loader says, you need version 21.0.x of BCLib (and WorldWeaver).

Note that you might want to hold off—the current version of BetterEnd is very much not ready for primetime (just look at the number of recent bug reports).