java.lang.RuntimeException: Could not execute entrypoint stage 'client' due to errors, provided by 'cameraoverhaul'!
at org.quiltmc.loader.impl.entrypoint.EntrypointUtils.lambda$invoke0$2(EntrypointUtils.java:63)
at org.quiltmc.loader.impl.util.ExceptionUtil.gatherExceptions(ExceptionUtil.java:33)
at org.quiltmc.loader.impl.entrypoint.EntrypointUtils.invoke0(EntrypointUtils.java:61)
at org.quiltmc.loader.impl.entrypoint.EntrypointUtils.invokeContainer(EntrypointUtils.java:46)
at org.quiltmc.loader.impl.entrypoint.EntrypointUtils.invoke(EntrypointUtils.java:33)
at org.quiltmc.loader.impl.game.minecraft.Hooks.startClient(Hooks.java:53)
at net.minecraft.class_310.(class_310.java:459)
at net.minecraft.client.main.Main.method_44604(Main.java:205)
at net.minecraft.client.main.Main.main(Main.java:51)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at org.quiltmc.loader.impl.game.minecraft.MinecraftGameProvider.launch(MinecraftGameProvider.java:423)
at org.quiltmc.loader.impl.launch.knot.Knot.launch(Knot.java:76)
at org.quiltmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:24)
Caused by: java.lang.RuntimeException: Mixin transformation of mirsario.cameraoverhaul.common.systems.CameraSystem failed
at org.quiltmc.loader.impl.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:283)
at org.quiltmc.loader.impl.launch.knot.KnotClassDelegate.tryLoadClass(KnotClassDelegate.java:153)
at org.quiltmc.loader.impl.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:156)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
at mirsario.cameraoverhaul.common.CameraOverhaul.onInitializeClient(CameraOverhaul.java:23)
at mirsario.cameraoverhaul.fabric.FabricClientModInitializer.onInitializeClient(FabricClientModInitializer.java:15)
at org.quiltmc.loader.impl.game.minecraft.Hooks.lambda$startClient$1(Hooks.java:53)
at org.quiltmc.loader.impl.entrypoint.EntrypointUtils.lambda$invoke$0(EntrypointUtils.java:33)
at org.quiltmc.loader.impl.entrypoint.EntrypointUtils.invoke0(EntrypointUtils.java:59)
... 13 more
Caused by: org.spongepowered.asm.mixin.transformer.throwables.MixinTransformerError: An unexpected critical error was encountered
at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:392)
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:234)
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:202)
at org.quiltmc.loader.impl.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:278)
... 21 more
Caused by: org.spongepowered.asm.mixin.injection.throwables.InjectionError: Critical injection failure: Argument modifier method doABarrelRoll$cancelYawDeltaRollOffset(F)F in do-a-barrel-roll.compat.cameraoverhaul.mixins.json:CameraSystemMixin from mod do_a_barrel_roll failed injection check, (0/1) succeeded. Scanned 1 target(s). Using refmap do-a-barrel-roll-fabric-refmap.json
at org.spongepowered.asm.mixin.injection.struct.InjectionInfo.postInject(InjectionInfo.java:468)
at org.spongepowered.asm.mixin.transformer.MixinTargetContext.applyInjections(MixinTargetContext.java:1385)
at org.spongepowered.asm.mixin.transformer.MixinApplicatorStandard.applyInjections(MixinApplicatorStandard.java:1052)
at org.spongepowered.asm.mixin.transformer.MixinApplicatorStandard.applyMixin(MixinApplicatorStandard.java:400)
at org.spongepowered.asm.mixin.transformer.MixinApplicatorStandard.apply(MixinApplicatorStandard.java:325)
at org.spongepowered.asm.mixin.transformer.TargetClassContext.apply(TargetClassContext.java:421)
at org.spongepowered.asm.mixin.transformer.TargetClassContext.applyMixins(TargetClassContext.java:403)
at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:363)
... 24 more

What versions of DABR and Camera Overhaul are you using?

Camera overhaul 1.3.1-fabric-universal & DABR-2.6.1-fabric

This isn't too important, just a preference thing, feel free to close if you deem this unnecessary.
:)

Ah, DABR contains a compatibility mixin that only works for Camera Overhaul 1.4.0+. The issue should fix itself if you get the latest version.

Oh I'm a numpty, cheers mate