The latest version (20.10.76) is adding Find & Merge back. I won’t be showing yellow box until I’m confident the feature works properly. It is rewritten from ground-up so it can be adapted to any tab (not just inventory items).
So for now, just look for Find & Merge button in the bottom-right corner under Inventory Items tab.
It fully supports History so if you make a mistake merging something you didn’t want to or the program did something wrong, you can undo the changes using undo function in History.