[Kanegasi]

This code runs every time you leave combat. This is fine, especially since some things may reset themselves in combat, but this also means you're creating several more function hooks (the hooksecurefunc). Let's say you get into and out of combat 100 times. Every time one of those fontstrings tries to show now, such as PlayerLevelText, the game calls PlayerLevelText:Hide() literally 100 times. Next time you leave combat adds another hook, calling :Hide() 101 times. You probably noticed the longer you played, the worse the lag was.

I removed the three buff lines, protected the hooks and the securestatedriver behind a switch so they only happen once, and cleaned up the code, including changing the function hooks into widget hooks. I'm not too familiar with securestatedriver stuff, but I'm pretty sure every time a specific register function is called, it toggles that state, so you should only call it once.

-- UI Scripts - Shadowlands updated - Emil
 
local f=CreateFrame("frame")
f:RegisterEvent("PLAYER_ENTERING_WORLD") --Event that fires on loadingscreens
f:RegisterEvent("PLAYER_REGEN_DISABLED")
f:RegisterEvent("PLAYER_REGEN_ENABLED")
f:SetScript("OnEvent",function(self,event,...)
    if event~="PLAYER_REGEN_DISABLED" then
 
        for _,v in pairs({"Character","Spellbook","Talent","Achievement","QuestLog","Guild","LFD","Collections","EJ","Store","MainMenu"}) do
            _G[v.."MicroButton"]:SetScale(.001)
        end
        MicroButtonAndBagsBar:Hide()
 
        PlayerFrame:SetScale(1.2)
        TargetFrame:SetScale(1.2)
        FocusFrame:SetScale(1.2)
 
        SetCVar("cameradistancemaxfactor",10)
 
        local m1 = "MultiBarBottomRight"
        _G[m1.."Button7"]:SetPoint("BOTTOMLEFT",_G[m1.."Button1"],"TOPLEFT",0,4)
        UIPARENT_MANAGED_FRAME_POSITIONS[m1].xOffset = 6
        ActionBarUpButton:Hide()
        MainMenuBar.GetYOffset=function() return -30 end
        UIParent_ManageFramePositions()
 
        local m2 = "MainMenuBarArtFrame"
        _G[m2.."Background"]:Hide()
        _G[m2].PageNumber:Hide()
        _G[m2].LeftEndCap:Hide()
        _G[m2].RightEndCap:Hide()
        ActionButton1:ClearAllPoints()
        ActionButton1:SetPoint("BOTTOM",_G[m2.."Background"],-340,35)
        ActionBarDownButton:Hide()
 
        if not f.hooks then
            for _,v in pairs({TargetFrame.levelText,FocusFrame.levelText,TargetFrame.name,PlayerFrame.name,FocusFrame.name,PlayerLevelText}) do
    --          hooksecurefunc(v,"Show",function(s) s:Hide() end)
                v:HookScript("OnShow",function(s) s:Hide() end)
                v:Hide()
            end
            RegisterStateDriver(StanceBarFrame,"visibility","hide")
            RegisterStateDriver(PetActionBarFrame,"visibility","hide")
            f.hooks=true
        end
 
        C_NamePlate.SetNamePlateFriendlySize(40,20)
 
        GameTimeFrame:Hide()
        MiniMapTrackingBackground:Hide()
        MiniMapTrackingButton:Hide()
        MiniMapTrackingIcon:Hide()
        MiniMapWorldMapButton:Hide()
        MinimapBorderTop:Hide()
        MinimapZoneText:Hide()
        MinimapZoomIn:Hide()
        MinimapZoomOut:Hide()
        PetActionBarFrame:Hide()
 
        -- Blizzard_TimeManager
        LoadAddOn("Blizzard_TimeManager")
        TimeManagerClockButton:Hide()
    end
end)