I have a mod that adds extra slot for totem of undying and elytra slot but they dont show, and this is a real dealbraker.

Closing in favor of #318

You can access the Trinkets menu by pressing a toggle in the top-right corner. It takes you from Inventorio menu to vanilla inventory menu, which trinkets modifies.

I mentioned that I have the same problem. Also, there is no button in the upper right corner.

ok i found the problem and i found a solution by myself, The green book under 2x2 production appears in the upper right,
clicking on this book will leave the inventorio inventory and switch to the normal vanilla inventory and the trinkets slots will appear, also the green book will go back to its old position. that toolbar does not appear due to a visual error, but it's there.