I am leaving the repository open for anyone interested. Resike has updated Trinket menu for both Wow Vanilla/Classic and TBC-Classic: TrinketMenu at Curseforge Old readme underneath.
The Trinket Menu addon for WoW, updated for Classic WoW 1.13
I have used the addon over at https://www.wowinterface.com/downloads/info24977-TrinketMenuClassic.html as a base.
Refer to readme.txt for the original addons instructions and update history.
Instructions in short: Mouse over the window for the selectable trinkets to pop up. Left click for top trinket, right click for bottom trinket. Rightclick the background around the trinket slots to change between Left/Right and Top/Bottom layout on the equippable trinkets. Middlemouseclick the background around the trinket slots to change between Left/Right and Top/Bottom layout on the equipped trinkets.
Install instructions: Download the master branch and unzip to a folder Move this folder to the "\Interface\Addons" folder. Make sure the "TrinketMenu.toc" file is directly under the TrinketMenu folder. In other words: "\Interface\Addons\TrinketMenu\TrinketMenu.toc"