The issue isn’t concatenation its game.Players[game.Players.LocalPlayer]. If there isn’t a particular reason why you’d need to index game.Players with the player instance then i would just do:
local points = game.Players.LocalPlayer.leaderstats.Points.Value
To properly reference the player all you need to do is the same thing but without game.Players[].
local player = game:GetService("Players").LocalPlayer -- Reference the player
local points = player.leaderstats.Points.Value -- Reference the points leaderstat in the player instance
script.Parent.Points.Frame.TextLabel.Text = "Points: " .. points
Also as @juliaoverflow stated if you ever need to convert something into a string you can just use the tostring() function (but its not needed in this scenario).