[Xrystal]

You have to initialise your saved variables .. by default they will be nil.

Near the top of your addon's lua file you need set the base values

-- This will create a new table containing no values
<SavedVariablePerCharacterTable> = {}

-- This will set the version variable to nil so that the first test will cause the splash to appear.
<SavedVariablePerCharacterTable>.version = nil

By the time PLAYER_ENTERING_WORLD is called your saved variables should be loaded in memory

So, using your example you posted this is how I would code it. See how this works out for you. Login a few times without changing the Version field in the TOC and then a few times after changing it ... the splash should only appear after it is changed.

local addonName, addonData = ...
 
-- Force initialisation in case there are no saved variables yet
-- These should get overriden when the saved variables are loaded
PawDB = {}
PawDB.version = nil
 
-- Event function
local function OnEvent(self,event,...)
 
      -- create variables from the event arguments
      local login,reload = ...
 
        -- if this is the first time entering the world
        if event == "PLAYER_ENTERING_WORLD" and login == true then
           local version = GetAddOnMetadata("PawsUI", "Version") 
            if version ~= PawDB.version then
                -- Show the Splash Frame and fill any of the UI with its required data
                self:SetSize(850, 480); -- the size of the splash
                self:SetPoint("CENTER"); -- its position on the screen            
                UIFrameFadeIn(self,1,0,1);
 
                -- Then Update the saved variable table for the character with the new version 
                PawDB.version = version
           end
      end
 end
 
-- Create the frame and set which events to monitor and which function will respond to it
local InstallerLogo = CreateFrame("Frame", addonName.."ILogo", UIParent);
InstallerLogo:RegisterEvent("PLAYER_ENTERING_WORLD");
InstallerLogo:SetScript("OnEvent", OnEvent)