[18:40:38] [Render thread/ERROR]: A mod tried to use the ImmediatelyFast batching API, but it is no longer available in 1.21.
[18:40:38] [Render thread/ERROR]: Mojang added basic batching into the DrawContext class. ImmediatelyFast now uses and extends this system, so this method is no longer needed.
[18:40:38] [Render thread/ERROR]: To migrate your mod, simply remove all calls to the ImmediatelyFast batching API and make sure to use the DrawContext for your HUD rendering.
[18:40:38] [Render thread/ERROR]: Here is a stack trace to help you find the offending code:
java.lang.Exception: null
at knot/net.raphimc.immediatelyfast.apiimpl.BatchingAccessImpl.warn(BatchingAccessImpl.java:66) ~[ImmediatelyFast-Fabric-1.9.5+1.21.5.jar:?]
at knot/net.raphimc.immediatelyfast.apiimpl.BatchingAccessImpl.isHudBatching(BatchingAccessImpl.java:43) ~[ImmediatelyFast-Fabric-1.9.5+1.21.5.jar:?]
at knot/gg.essential.compat.ImmediatelyFastCompat.beforeHudDraw(ImmediatelyFastCompat.java:42) ~[Essential%20(fabric_1.21.5).jar:?]
at knot/gg.essential.handlers.OnlineIndicator.beforeTabDraw(OnlineIndicator.java:178) ~[Essential%20(fabric_1.21.5).jar:?]
at knot/gg.essential.cosmetics.IconCosmeticRenderer.drawTextureInTabList(IconCosmeticRenderer.kt:361) ~[Essential%20(fabric_1.21.5).jar:?]
at knot/gg.essential.handlers.OnlineIndicator.drawTabIndicator(OnlineIndicator.java:134) ~[Essential%20(fabric_1.21.5).jar:?]
at knot/gg.essential.handlers.OnlineIndicator.drawTabIndicatorOuter(OnlineIndicator.java:103) ~[Essential%20(fabric_1.21.5).jar:?]
at knot//MC/net.minecraft.client.gui.hud.PlayerListHud.modify$dkb000$essential$shiftNameTextAndRenderIcon(PlayerListHud.java:590) ~[client-intermediary.jar:?]
at knot//MC/net.minecraft.client.gui.hud.PlayerListHud.render(PlayerListHud.java:234) ~[client-intermediary.jar:?]
at knot//MC/net.minecraft.client.gui.hud.InGameHud.renderPlayerList(InGameHud.java:404) ~[client-intermediary.jar:?]
at knot/net.fabricmc.fabric.impl.client.rendering.WrappedLayer.render(WrappedLayer.java:35) ~[fabric-rendering-v1-11.2.0+acfc689549-ed92a36c0e1cb62.jar:?]
at knot//MC/net.minecraft.client.gui.LayeredDrawer.renderInternal(LayeredDrawer.java:36) ~[client-intermediary.jar:?]
at knot//MC/net.minecraft.client.gui.LayeredDrawer.invokeRenderInternal(LayeredDrawer.java) ~[client-intermediary.jar:?]
at knot/net.fabricmc.fabric.impl.client.rendering.SubLayer.render(SubLayer.java:43) ~[fabric-rendering-v1-11.2.0+acfc689549-ed92a36c0e1cb62.jar:?]
at knot//MC/net.minecraft.client.gui.LayeredDrawer.renderInternal(LayeredDrawer.java:36) ~[client-intermediary.jar:?]
at knot//MC/net.minecraft.client.gui.LayeredDrawer.render(LayeredDrawer.java:29) ~[client-intermediary.jar:?]
at knot//MC/net.minecraft.client.gui.hud.InGameHud.render$mixinextras$wrapped$109(InGameHud.java:235) ~[client-intermediary.jar:?]
at knot//MC/net.minecraft.client.gui.hud.InGameHud.mixinextras$bridge$method_1753$mixinextras$wrapped$109$110(InGameHud.java) ~[client-intermediary.jar:?]
at knot//MC/net.minecraft.client.gui.hud.InGameHud.wrapMethod$blk000$iris$handleHudHidingScreens(InGameHud.java:5066) ~[client-intermediary.jar:?]
at knot//MC/net.minecraft.client.gui.hud.InGameHud.render(InGameHud.java) ~[client-intermediary.jar:?]
at knot//MC/net.minecraft.client.render.GameRenderer.mixinextras$bridge$method_1753$91(GameRenderer.java) ~[client-intermediary.jar:?]
at knot//MC/net.minecraft.client.render.GameRenderer.wrapOperation$bhg000$immediatelyfast$hudBatching(GameRenderer.java:2919) [client-intermediary.jar:?]
at knot//MC/net.minecraft.client.render.GameRenderer.render(GameRenderer.java:554) [client-intermediary.jar:?]
at knot//MC/net.minecraft.client.MinecraftClient.render(MinecraftClient.java:1353) [client-intermediary.jar:?]
at knot//MC/net.minecraft.client.MinecraftClient.run(MinecraftClient.java:936) [client-intermediary.jar:?]
at knot/net.minecraft.client.main.Main.main(Main.java:265) [client-intermediary.jar:?]
at net.fabricmc.loader.impl.game.minecraft.MinecraftGameProvider.launch(MinecraftGameProvider.java:480) [fabric-loader-0.16.14.jar:?]
at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:74) [fabric-loader-0.16.14.jar:?]
at net.fabricmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:23) [fabric-loader-0.16.14.jar:?]

This is caused by a mod (Essential) using ImmediatelyFast API which no longer exists. You have to report it to them

This stack trace does indeed not have any impact on gameplay or performance