With default settings:

With following settings:

With different settings:

(Black bars are part of mc)
Slide in from bottom and fade in are both enabled.
Please let me know if you need any more info.
My other mods:

[✔️] advancements-enlarger-0.2.4
[✔️] amecs-1.3.4+mc.1.17
[✔️] antighost-1.17.1-fabric0.36.1-1.1.4
[✔️] anti-night-vision-flash-1.0.0
[✔️] appleskin-fabric-mc1.17-2.1.3
[✔️] architectury-2.5.27-fabric
[✔️] audiooutput-0.0.4
[✔️] badstdout-1.1.0-1.17
[✔️] betterbeds-1.2.0
[✔️] betterf3-1.1.5+1.17
[❌] bsvsb-2.0.2.jar (disabled)
[✔️] carpet-extra-1.17.1-1.4.43
[✔️] cem-0.6.2
[✔️] cherishedworlds-fabric-2.0.1-1.17.1
[✔️] clear-skies-mc117-1.5.70
[✔️] clientcommands-2.5.4
[✔️] cloth-api-2.0.54
[✔️] cloth-config-5.0.38-fabric
[❌] colormatic-2.2.10+mc.1.17.1.jar (disabled)
[✔️] completeconfig-lib-1.1.0
[✔️] connected-block-textures-0.1.5+1.17
[✔️] Controlling-For-Fabric-1.2.0
[✔️] CraftPresence-Fabric-1.17.1-Release-1.8.4
[✔️] cullleaves-2.2.0
[✔️] customsplashscreen-1.1.0
[❌] DraggableResourcePacks-1.0.1.jar (disabled)
[✔️] dynamic-fps-2.0.5
[✔️] enhanced_attack_indicator-1.0.2+1.17
[✔️] EntityCulling-Fabric-1.3.3
[✔️] Fabric-1.17.1-TimeToLive-0.4
[✔️] fabric-api-0.40.1+1.17
[✔️] fabric-carpet-1.17.1-1.4.45+v210811
[✔️] fabric-death-coords-1.17.1-1.0.0
[✔️] fabric-language-kotlin-1.6.4+kotlin.1.5.30
[✔️] fabric-mumblelink-mod-0.8.4
[✔️] fabricskyboxes-1.17-0.5.2
[✔️] ferritecore-3.0.3-fabric
[✔️] figura-0.0.6-1.17.x
[✔️] horse-stats-vanilla-4.1.8
[✔️] hydrogen-fabric-mc1.17.1-0.3
[❌] indium-1.0.0+mc1.17.1.jar (disabled)
[✔️] inspecio-1.1.0+1.17
[❌] iris-and-sodium-mc1.17-1.1.2+build.9.jar (disabled)
[✔️] item-model-fix-1.0.2+1.17
[✔️] krypton-0.1.4
[✔️] lambdabettergrass-1.2.1+1.17
[✔️] lambdynamiclights-2.0.2+1.17
[✔️] lazydfu-0.1.2
[✔️] light-overlay-6.0.0-fabric
[✔️] lithium-fabric-mc1.17.1-0.7.4
[✔️] mcpppp-0.4.0
[✔️] mixintrace-1.1.0+1.17
[✔️] modmenu-2.0.10
[✔️] mousewheelie-1.7.3+mc1.17.1-pre1
[✔️] multiconnect-1.4.15
[✔️] notenoughanimations-1.3.0
[✔️] notenoughcrashes-3.4.4+1.17-fabric
[✔️] okzoomer-5.0.0-beta.2+1.17
[✔️] PerspectiveModRedux-1.17-0.0.5_01
[✔️] pling-1.4.0
[✔️] PresenceFootsteps-r32-1.17-rc1
[✔️] recipecache-0.2.0-1.17.1
[✔️] resolution-control-plus-3.0.0
[✔️] sheepconsistency-1.0.3
[✔️] slight-gui-modifications-2.0.1
[✔️] smoothboot-fabric-1.16.5-1.6.0
[❌] sodium-extra-mc1.17.1-0.3.4.jar (disabled)
[❌] sodium-fabric-mc1.17.1-0.3.2+build.7.jar (disabled)
[✔️] someforgepatchesported-1.0.1
[✔️] spark-fabric
[✔️] starlight-1.0.0-RC3+fabric.1.17.x
[✔️] stendhal-1.2.0-1.17.1
[✔️] TRansliterationLib-1.1.0
[✔️] uglyscoreboardfix-2.3.1
[✔️] visualoverhaul-3.3.0
[✔️] yosbr-0.1.1

I have already tried without custom splash screen and the issue persists, but black bars are red.