[Fizzlemizz]

Install BugGrabber and BugSack so you can see the errors you are getting.

You've created LastLoginTrackerTextLabel as a global variable

LastLoginTrackerTextLabel = frame:CreateFontString(nil, "OVERLAY", "GameFontHighlight")

But you're accessing it in UpdateLastLogin() as if it was created as a sub-key of frame

Three problems:
1. UpdateLastLogin can't access frame because it is a local variable created AFTER the function has been declared ie. it is out-of-scope

2. Once one is fixed you would need to change LastLoginTrackerTextLabel to be a sub-key of frame.

3. You're redeclaring the frame variable to create a second unnecessary frame (well, the first is unnecessary as LastLoginTrackerFrame can do event registration/handling).

The code adjusted to pass self:GetParent() (The parent of the button which is frame) to the functions and use that. Also remove the first frame as the as you were registering the event on that one but setting the OnEvent script on the second, LastLoginTrackerFrame (through redeclaring the local frame variable) meaning PLAYER_LOGIN would never have fired.

-- LastLoginTracker.lua
 
-- Function to initialize or load saved last login time
local function InitializeLastLogin()
    if not LastLoginTrackerDB then
        LastLoginTrackerDB = {}
    end
 
    if not LastLoginTrackerDB.lastLoginTime then
        LastLoginTrackerDB.lastLoginTime = time()
    end
end
 
-- Function to update and display last login time
local function UpdateLastLogin(self)
    LastLoginTrackerDB.lastLoginTime = time()
    local formattedTime = date("%H:%M:%S", LastLoginTrackerDB.lastLoginTime)
    print("Last Login: " .. formattedTime)
    self.LastLoginTrackerTextLabel:SetText("Last Login: " .. formattedTime)
end
 
-- Create a simple form with a button
local frame = CreateFrame("Frame", "LastLoginTrackerFrame", UIParent, "BasicFrameTemplate")
frame:SetSize(250, 100)
frame:SetPoint("CENTER")
frame:Hide()
frame:RegisterEvent("PLAYER_LOGIN")
 
frame.title = frame:CreateFontString(nil, "OVERLAY", "GameFontHighlight")
frame.title:SetPoint("CENTER", frame.TitleBg, "CENTER", 0, 0)
frame.title:SetText("Last Login Tracker")
 
-- Create a button to update last login time
frame.LastLoginTrackerButton = CreateFrame("Button", nil, frame, "GameMenuButtonTemplate")
frame.LastLoginTrackerButton:SetSize(200, 25)
frame.LastLoginTrackerButton:SetPoint("CENTER", frame, "CENTER", 0, 0)
frame.LastLoginTrackerButton:SetText("Update Last Login")
frame.LastLoginTrackerButton:SetNormalFontObject("GameFontNormal")
 
-- Create a text label to display last login time
frame.LastLoginTrackerTextLabel = frame:CreateFontString(nil, "OVERLAY", "GameFontHighlight")
frame.LastLoginTrackerTextLabel:SetPoint("CENTER", frame, "CENTER", 0, -20)
frame.LastLoginTrackerTextLabel:SetText("Last Login: Not tracked")
 
-- Set up event handling for the button
frame.LastLoginTrackerButton:SetScript("OnClick", function(self, button, down)
    UpdateLastLogin(self:GetParent())
end)
 
-- Event handler for PLAYER_LOGIN
frame:SetScript("OnEvent", function(self, event, arg1)
    if event == "PLAYER_LOGIN" then
        InitializeLastLogin()
    end
end)
 
-- Slash command to show/hide the form
SLASH_LASTLOGINTRACKER1 = "/lastlogin"
SlashCmdList["LASTLOGINTRACKER"] = function()
    frame:SetShown(not frame:IsShown())
end