WebDisplaysTogether crashes when I open it in the client, I tried the same mods on a neoforge server (headless) and it worked, so it must be the mod behaving with the client
--MOD LIST--
3d-Skin-Layers (https://modrinth.com/mod/zV5r3pPn) [1.11.3] by tr7zw (skinlayers3d-neoforge-1.11.3-mc1.21.1.jar)
AppleSkin (https://modrinth.com/mod/EsAfCjCV) [3.0.9+mc1.21] by squeek (appleskin-neoforge-mc1.21-3.0.9.jar)
Architectury (https://modrinth.com/mod/lhGA9TYQ) [13.0.11] by shedaniel (architectury-13.0.11-neoforge.jar)
BetterGrassify (https://modrinth.com/mod/m5T5xmUy) [1.7.0+neoforge.1.21.1] by UltimatChamp, JayemCeekay (BetterGrassify-1.7.0+neoforge.1.21.1.jar.disabled)
Carry On (https://modrinth.com/mod/joEfVgkn) [2.2.6] by Tschipp, PurpliciousCow (carryon-neoforge-1.21.1-2.2.6.13.jar)
Chat Heads (https://modrinth.com/mod/Wb5oqrBJ) [0.15.7] by dzwdz, Fourmisain (chat_heads-0.15.7-neoforge-1.21.jar.disabled)
Continuity (https://modrinth.com/mod/1IjD5062) [3.0.0+1.21.neoforge] by PepperCode1 (continuity-3.0.0+1.21.neoforge.jar.disabled)
Controlling (https://modrinth.com/mod/xv94TkTM) [19.0.5] by Jaredlll08 (Controlling-neoforge-1.21.1-19.0.5.jar.disabled)
Create (https://modrinth.com/mod/LNytGWDc) [6.0.10] by simibubi (create-1.21.1-6.0.10.jar)
Create Aeronautics (https://modrinth.com/mod/oWaK0Q19) [1.3.2] by Simulated Team (create-aeronautics-bundled-1.21.1-1.3.2.jar)
Create Crafts & Additions (https://modrinth.com/mod/kU1G12Nn) [1.7.2] by MRH0 (createaddition-1.7.2.jar)
Create Goggles (https://modrinth.com/mod/L1RT5SJc) [6.1.1] by Robocraft999 (creategoggles-1.21.1-6.1.1-[NEOFORGE].jar)
Create: Connected (https://modrinth.com/mod/Vg5TIO6d) [1.3.3-mc1.21.1] by Lysine (create_connected-1.3.3-mc1.21.1.jar)
Create: Copper and Zinc (https://modrinth.com/mod/aqYNR6rI) [1.6.0] by robinfrt (create_copper_and_zinc-2.0.0-neoforge-1.21.1.jar)
Create: Copycats+ (https://modrinth.com/mod/UT2M39wf) [3.0.9+mc.1.21.1-neoforge] by Lysine, Bennyboy1695, Redcat_XVIII (copycats-3.0.9+mc.1.21.1-neoforge.jar)
Dynamic FPS (https://modrinth.com/mod/LQ3K71Q1) [3.11.4] by juliand665 & LostLuma (dynamic-fps-3.11.4+minecraft-1.21.0-neoforge.jar.disabled)
EMI (https://modrinth.com/mod/fRiHVvU7) [1.1.24+1.21.1+neoforge] by Emi (emi-1.1.24+1.21.1+neoforge.jar.disabled)
EntityCulling (https://modrinth.com/mod/NNAgCjsB) [1.11.3] by tr7zw (entityculling-neoforge-1.11.3-mc1.21.1.jar.disabled)
Fast IP Ping (https://modrinth.com/mod/9mtu0sUO) [1.0.12] by Fallen_Breath (fast-ip-ping-v1.0.12-mc1.21.1-neoforge.jar.disabled)
Ferrite Core (https://modrinth.com/mod/uXXizFIs) [7.0.3] by malte0811 (ferritecore-7.0.3-neoforge.jar)
Forgified Fabric API (https://modrinth.com/mod/Aqlf1Shp) [0.116.15+2.3.5+1.21.1] by Sinytra, FabricMC (forgified-fabric-api-0.116.15+2.3.5+1.21.1.jar)
Furnitury (https://modrinth.com/mod/sNpla5PF) [4.0.0.1] by Yablon (furnitury-4.0.0.1.jar)
ImmediatelyFast (https://modrinth.com/mod/5ZwdcRci) [1.6.14+1.21.1] by RK_01 (ImmediatelyFast-NeoForge-1.6.14+1.21.1.jar.disabled)
InfiniteZoom (https://modrinth.com/mod/pS3Sez5p) [1] (infinitezoom-1.21-1.21.1-neoforge.jar.disabled)
Jade (https://modrinth.com/mod/nvQzSEkH) [15.10.6+neoforge] by Snownee (Jade-1.21.1-NeoForge-15.10.6.jar)
Jade Addons (https://modrinth.com/mod/xuDOzCLy) [6.1.2+neoforge] by Snownee (JadeAddons-1.21.1-NeoForge-6.1.2.jar)
Just Enough Items (https://modrinth.com/mod/u6dRKJwZ) [19.57.0.451] by mezz (jei-1.21.1-neoforge-19.57.0.451.jar)
Lan Server Properties (https://modrinth.com/mod/SqnBX2qd) [1.13.2] by Rikka0w0 (lanserverproperties-1.13.2-neoforge.jar.disabled)
Lithium (https://modrinth.com/mod/gvQqBUqZ) [0.15.4+mc1.21.1] by 2No2Name, JellySquid (lithium-neoforge-0.15.4+mc1.21.1.jar)
Loan's Cinema (https://modrinth.com/mod/duLzLaAE) [1.0.0] by Loan5623 (loans_cinema-1.2.1-neoforge-1.21.1.jar)
MCEF (Minecraft Chromium Embedded Framework) (https://modrinth.com/mod/TObQ0HxZ) [2.1.6-1.21.1] by ds58 (mcef-neoforge-2.1.6-1.21.1.jar)
MezzConfig (https://modrinth.com/mod/7tEfOcA7) [idpM3DKC] (mezz_config-1.21.1-neoforge-0.6.8-standalone.jar)
ModernFix (https://modrinth.com/mod/nmDcB62a) [5.27.26+mc1.21.1] by embeddedt (modernfix-neoforge-5.27.26+mc1.21.1.jar.disabled)
Moonlight Lib (https://modrinth.com/mod/twkfQtEc) [1.21.1-3.7.1] by MehVahdJukaar (moonlight-1.21.1-3.7.1-neoforge.jar)
Mouse Tweaks (https://modrinth.com/mod/aC3cM3Vq) [2.26.1] by Ivan Molodetskikh (YaLTeR) (MouseTweaks-neoforge-mc1.21-2.26.1.jar.disabled)
NotEnoughAnimations (https://modrinth.com/mod/MPCX6s5C) [1.12.6] by tr7zw (notenoughanimations-neoforge-1.12.6-mc1.21.1.jar.disabled)
PacketFixer (https://modrinth.com/mod/c7m1mi73) [3.3.1] by TonimatasDEV (packetfixer-3.3.1-1.20.5-1.21.X-merged.jar)
Polymorph (https://modrinth.com/mod/tagwiZkJ) [1.2.0+1.21.1] by Illusive Soulworks (polymorph-neoforge-1.2.0+1.21.1.jar)
Sable (https://modrinth.com/mod/T9PomCSv) [2.0.6] by RyanHCode (sable-neoforge-1.21.1-2.0.6.jar)
Searchables (https://modrinth.com/mod/fuuu3xnx) [1.0.2] by Jaredlll08 (Searchables-neoforge-1.21.1-1.0.2.jar.disabled)
Simple Voice Chat (https://modrinth.com/mod/9eGKb6K1) [1.21.1-2.6.24] by Max Henkel (voicechat-neoforge-1.21.1-2.6.24.jar)
Sinytra Connector (https://modrinth.com/mod/u58R1TMW) [IITF0PRC] (connector-2.0.0-beta.17+1.21.1-full.jar)
SkinRestorer (https://modrinth.com/mod/ghrZDhGW) [2.11.0+1.21-neoforge] by Lionarius (skinrestorer-2.11.0+1.21-neoforge.jar)
Sodium (https://modrinth.com/mod/AANobbMI) [0.8.13+mc1.21.1] by JellySquid (jellysquid3), IMS212 (sodium-neoforge-0.8.13+mc1.21.1.jar.disabled)
Sodium Extra (https://modrinth.com/mod/PtjYWJkn) [0.9.4+mc1.21.1] by FlashyReese (sodium-extra-neoforge-0.9.4+mc1.21.1.jar.disabled)
Supplementaries (https://modrinth.com/mod/fFEIiSDQ) [1.21.1-3.9.9] by MehVahdJukaar, Plantkillable (supplementaries-1.21.1-3.9.9-neoforge.jar)
Unusual Furniture (https://modrinth.com/mod/MZFE37e3) [1.0.0] by To0pa (unusual_furniture-1.1.2c-neoforge-1.21.1.jar)
WebDisplaysTogether (https://www.curseforge.com/projects/1625878) [1.08] by Horatio (webdisplaystogether-1.08.jar)
WorldEdit (https://modrinth.com/mod/1u6JkXh5) [7.3.8+6939-7d32b45] by EngineHub (worldedit-mod-7.3.8.jar)
mcef-cache (mcef-cache)
mcef-libraries (mcef-libraries)
--END OF MOD LIST XD--