[SDPhantom]

Not sure if RequiredDeps is the right tag to use when the target is a LoD addon. You should use LoadWith instead.

## LoadOnDemand: 1
## LoadWith: Blizzard_Collections

Also, the specific way CollectionsJournal_UpdateSelectedTab() is written, you don't need to replace it. You can secure hook it and add your own code to show your own tab.

Here's an example:

local TabName="MyNewTab";
 
local TabID=CollectionsJournal.numTabs+1;
local Tab=CreateFrame("Button","$parentTab"..TabID,CollectionsJournal,"CollectionsJournalTab",TabID);
PanelTemplates_SetNumTabs(CollectionsJournal,TabID);
Tab:SetPoint("LEFT","$parentTab"..(TabID-1),"RIGHT",-16,0);
Tab:SetText(TabName);
 
local Panel=CreateFrame("Frame",nil,CollectionsJournal);
Panel:SetAllPoints(CollectionsJournal);
 
hooksecurefunc("CollectionsJournal_UpdateSelectedTab",function(self)
    local selected=PanelTemplates_GetSelectedTab(self);
    if selected==TabID then CollectionsJournalTitleText:SetText(TabName); end
    Panel:SetShown(selected==TabID);
end);

Panel is the frame you'll want to build your UI on and it also plays nice with any other addon that wants to create their own tab on the CollectionsJournal.