Doesn't a server-sided script creating a GUI make it visible to everyone?

1. What do you want to achieve?

I have a button and when the button is clicked it actives a remote event which leads straight to the server. In the server script, it creates an 'imageLabel' and then sets the player's head to the imageLabel. However, as it is server-sided I expected it to show for everyone, however, it only shows for the local player.

1. What is the issue?

The only issue is that it only shows in the client's screen, but doesn't show everywhere else. I want it to show the local player who clicked the button on everyone's screen.

1. What solutions have you tried so far?

I've looked everywhere for the solution to my problem but haven't come across anything, that's why I resulted to trying here.

This is what I have tried:

Local script:

script.Parent.readyToStart.MouseButton1Click:Connect(function(player)
	remoteEventPlayer:FireServer(player)
end)

Server script:

local remoteEventLocalPhoto = game.ReplicatedStorage.robloxLocalPhoto

local function playerPhoto(player)
	--setting up the image label
	print(player.Name)
	local remoteEventLocalPhoto = game.ReplicatedStorage.robloxLocalPhoto
	local typingChallenge = player.PlayerGui.typingChallenge
	local otherRacePosition = typingChallenge.otherRacePosition
	local newImage = Instance.new("ImageLabel", otherRacePosition)
	newImage.Name = player.Name
	newImage.Position = UDim2.new(0, 0,0, 0)
	newImage.Size = UDim2.new(0.06, 0,0.998, 0)
	newImage.BackgroundTransparency = 1
	
	-- setting the image label to the player's head
	local UserId = player.UserId
	local thumbType = Enum.ThumbnailType.HeadShot
	local thumbSize = Enum.ThumbnailSize.Size100x100
	local players = game:GetService("Players")
	local content, isReady = players:GetUserThumbnailAsync(UserId, thumbType, thumbSize)
	newImage.Image = content
end

remoteEventLocalPhoto.OnServerEvent:Connect(playerPhoto)

script.Parent.readyToStart.MouseButton1Click:Connect(function() -- this breaks the full script
    remoteEventPlayer:FireServer() -- dont put player there its not needed
end)

that's all, everything else is fine

Your problem is that OnServerEvent passes only the player that fired it, and other optional arguments, to fix this you have to loop between every player to get the desired effect. Your server script should look like:

local remoteEventLocalPhoto = game.ReplicatedStorage.robloxLocalPhoto
local players = game:GetService("Players")

local function playerPhoto(receivingplayer, sendingplayer)
    --setting up the image label
    print(receivingplayer.Name)
    local remoteEventLocalPhoto = game.ReplicatedStorage.robloxLocalPhoto
    local typingChallenge = receivingplayer.PlayerGui.typingChallenge
    local otherRacePosition = typingChallenge.otherRacePosition
    local newImage = Instance.new("ImageLabel", otherRacePosition)
    newImage.Name = sendingplayer.Name
    newImage.Position = UDim2.new(0, 0,0, 0)
    newImage.Size = UDim2.new(0.06, 0,0.998, 0)
    newImage.BackgroundTransparency = 1

    -- setting the image label to the player's head
    local UserId = sendingplayer.UserId
    local thumbType = Enum.ThumbnailType.HeadShot
    local thumbSize = Enum.ThumbnailSize.Size100x100
    local content, isReady = players:GetUserThumbnailAsync(UserId, thumbType, thumbSize)
    newImage.Image = content
end

remoteEventLocalPhoto.OnServerEvent:Connect(function(player)
	--loop a table of every player
	for i, v in pairs (players:GetPlayers()) do
		playerPhoto(v, player)
	end
end)

Edit: You also do not need to pass the LocalPlayer in :FireServer(), as it is already the first parameter in OnServerEvent