I am trying to remove the default roblox loading screen, the one that says "Joining server", I think i saw something like this on a game called "Island Royale" where it teleports you to an other place but he made his own custom gui for it.
Try this: https://developer.roblox.com/en-us/api-reference/function/ReplicatedFirst/RemoveDefaultLoadingScreen
To remove on-join, use:
--[[LocalScript in ReplicatedFirst]] game:GetService("ReplicatedFirst"):RemoveDefaultLoadingScreen();
When teleporting between places use the parameter customLoadingScreen in
TeleportService:Teleport -- OR TeleportService:TeleportPartyAsync -- OR TeleportService:TeleportToPrivateServer -- and etc..
Thanks for reading, hope this helps!