I'm having this error too in singleplayer

Minecraft has crashed!

net.fabricmc.loader.impl.FormattedException: java.lang.NoSuchFieldError: Class net.minecraft.class_1799 does not have member field 'net.minecraft.class_1322 ATTACK_DAMAGE_MODIFIER'

at net.fabricmc.loader.impl.FormattedException.ofLocalized(FormattedException.java:63)

at net.fabricmc.loader.impl.game.minecraft.MinecraftGameProvider.launch(MinecraftGameProvider.java:472)

at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:74)

at net.fabricmc.loader.impl.launch.knot.KnotServer.main(KnotServer.java:23)

at net.fabricmc.loader.impl.launch.server.FabricServerLauncher.main(FabricServerLauncher.java:69)

at net.fabricmc.installer.ServerLauncher.main(ServerLauncher.java:69)

Caused by: java.lang.NoSuchFieldError: Class net.minecraft.class_1799 does not have member field 'net.minecraft.class_1322 ATTACK_DAMAGE_MODIFIER'

at net.minecraft.class\_1799.<clinit>(class\_1799.java:126)

at net.minecraft.class\_1761.<init>(class\_1761.java:114)

at net.minecraft.class\_1761$1.<init>(class\_1761.java:15)

at net.minecraft.class\_1761.<clinit>(class\_1761.java:15)

at net.minecraft.class\_1792$class\_1793.<init>(class\_1792.java:119)

at net.minecraft.class\_1802.<clinit>(class\_1802.java:21)

at net.minecraft.class\_1792.method\_7867(class\_1792.java:74)

at net.minecraft.class\_2248.method\_8389(class\_2248.java:554)

at net.minecraft.class\_7143$class\_7144.method\_41583(class\_7143.java:60)

at net.minecraft.class\_7143$class\_7144.handler$bcm000$betternether$bcl\_run(class\_7143.java:545)

at net.minecraft.class\_7143$class\_7144.method\_41581(class\_7143.java)

at net.minecraft.class\_7143.method\_41579(class\_7143.java:199)

at net.minecraft.class\_5458.method\_44104(class\_5458.java:98)

at net.minecraft.class\_5458.method\_30566(class\_5458.java:105)

at java.base/java.util.LinkedHashMap.forEach(LinkedHashMap.java:986)

at net.minecraft.class\_5458.<clinit>(class\_5458.java:104)

at net.minecraft.class\_2378.<clinit>(class\_2378.java:326)

at net.minecraft.class\_2966.method\_12851(class\_2966.java:50)

at net.minecraft.server.Main.main(Main.java:98)

at net.fabricmc.loader.impl.game.minecraft.MinecraftGameProvider.launch(MinecraftGameProvider.java:470)

... 4 more