I was told to post my debug log so here it is.
[19:18:41] [main/INFO]: ModLauncher 3.2.0+60+b86c1d4 starting: java version 1.8.0_51 by Oracle Corporation
[19:18:42] [main/INFO]: OptiFineTransformationService.onLoad
[19:18:42] [main/INFO]: OptiFine ZIP file: C:\Users\Conno\Twitch\Minecraft\Instances\yeet\mods\OptiFine_1.14.4_HD_U_F5.jar
[19:18:42] [main/INFO]: Added Lets Encrypt root certificates as additional trust
[19:18:42] [main/INFO]: OptiFineTransformationService.initialize
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: org.spongepowered.asm.service.ServiceNotAvailableError: No mixin host service is available. Services: INVALID[ModLauncher] and 1 other invalid services.
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at org.spongepowered.asm.service.MixinService.initService(MixinService.java:159)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at org.spongepowered.asm.service.MixinService.getServiceInstance(MixinService.java:125)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at org.spongepowered.asm.service.MixinService.getService(MixinService.java:120)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at org.spongepowered.asm.launch.MixinBootstrap.(MixinBootstrap.java:78)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at org.spongepowered.asm.launch.MixinTransformationService.initialize(MixinTransformationService.java:84)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at io.github.lxgaming.mixin.launch.MixinTransformationService.lambda$initialize$2(MixinTransformationService.java:81)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at io.github.lxgaming.mixin.launch.MixinTransformationService$$Lambda$143/1631086936.accept(Unknown Source)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at java.lang.Iterable.forEach(Iterable.java:75)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at io.github.lxgaming.mixin.launch.MixinTransformationService.initialize(MixinTransformationService.java:81)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at cpw.mods.modlauncher.TransformationServiceDecorator.onInitialize(TransformationServiceDecorator.java:67)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at cpw.mods.modlauncher.TransformationServicesHandler.lambda$initialiseTransformationServices$7(TransformationServicesHandler.java:106)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at cpw.mods.modlauncher.TransformationServicesHandler$$Lambda$85/1069716895.accept(Unknown Source)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at java.util.HashMap$Values.forEach(HashMap.java:972)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at cpw.mods.modlauncher.TransformationServicesHandler.initialiseTransformationServices(TransformationServicesHandler.java:106)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at cpw.mods.modlauncher.TransformationServicesHandler.initializeTransformationServices(TransformationServicesHandler.java:59)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at cpw.mods.modlauncher.Launcher.run(Launcher.java:75)
[19:18:42] [main/INFO]: [java.lang.ThreadGroup:uncaughtException:1052]: at cpw.mods.modlauncher.Launcher.main(Launcher.java:65)

Update Forge.
Mixin requires ModLauncher v4.1 or higher which is only available in Forge 28.1.45 and above

Update Forge.
Mixin requires ModLauncher v4.1 or higher which is only available in Forge 28.1.45 and above

I did what you said, but this happened.

java.lang.NullPointerException: Rendering overlay
at net.minecraft.client.renderer.FluidBlockRenderer.func_178268_a(FluidBlockRenderer.java:41) ~[?:?] {re:classloading,xf:OptiFine:default}
at net.minecraft.client.renderer.BlockRendererDispatcher.func_195410_a(BlockRendererDispatcher.java:154) ~[?:?] {re:classloading,xf:OptiFine:default}
at net.minecraft.resources.IResourceManagerReloadListener.lambda$reload$0(IResourceManagerReloadListener.java:16) ~[?:?] {re:classloading,re:mixin}
at net.minecraft.resources.IResourceManagerReloadListener$$Lambda$2569/210282562.run(Unknown Source) ~[?:?] {}
at java.util.concurrent.CompletableFuture.uniRun(CompletableFuture.java:705) ~[?:1.8.0_51] {}
at java.util.concurrent.CompletableFuture$UniRun.tryFire(CompletableFuture.java:687) ~[?:1.8.0_51] {}
at java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:442) ~[?:1.8.0_51] {}
at net.minecraft.resources.AsyncReloader.func_219557_a(SourceFile:71) ~[?:?] {re:classloading}
at net.minecraft.resources.AsyncReloader$$Lambda$2808/2114020759.run(Unknown Source) ~[?:?] {}
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213166_h(ThreadTaskExecutor.java:170) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,xf:OptiFine:default}
at net.minecraft.util.concurrent.RecursiveEventLoop.func_213166_h(SourceFile:23) ~[?:?] {re:mixin,re:classloading}
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213168_p(ThreadTaskExecutor.java:135) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,xf:OptiFine:default}
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213160_bf(ThreadTaskExecutor.java:115) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,xf:OptiFine:default}
at net.minecraft.client.Minecraft.func_195542_b(Minecraft.java:861) [?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:A,pl:runtimedistcleaner:A}
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:384) [?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:A,pl:runtimedistcleaner:A}
at net.minecraft.client.main.Main.main(SourceFile:155) [?:?] {re:classloading}
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_51] {}
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_51] {}
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_51] {}
at java.lang.reflect.Method.invoke(Method.java:497) ~[?:1.8.0_51] {}
at net.minecraftforge.fml.loading.FMLClientLaunchProvider.lambda$launchService$0(FMLClientLaunchProvider.java:56) [forge-1.14.4-28.2.3.jar:28.2] {}
at net.minecraftforge.fml.loading.FMLClientLaunchProvider$$Lambda$460/1275011461.call(Unknown Source) [forge-1.14.4-28.2.3.jar:28.2] {}
at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) [modlauncher-4.1.0.jar:?] {}
at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:54) [modlauncher-4.1.0.jar:?] {}
at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:72) [modlauncher-4.1.0.jar:?] {}
at cpw.mods.modlauncher.Launcher.run(Launcher.java:81) [modlauncher-4.1.0.jar:?] {}
at cpw.mods.modlauncher.Launcher.main(Launcher.java:65) [modlauncher-4.1.0.jar:?] {}

Try recommended Forge (28.2.0) as mentioned here sp614x/optifine#3490

According to the issue I linked OptiFine isn't compatible with Forge 28.2.3, Hence why I said to downgrade to Forge 28.2.0 cause that version should be compatible with MixinBootstrap and OptiFine

I am trying 28.2.3 though...

I'm assuming the issue has been resolved, If not then reply in this thread.