Hi,
I recently installed Adibags and i was looking for a Sort bag button but i appears that mine does not show.
Is there is none in the new update or does need to do something to make it show?

A sorting function hasn't been implemented for the Classic version. The Retail version uses Blizzard's sort function which isn't available on the Classic client.

Ok thanks

kind of related question: if items aren't stacked optimally, does this addon restack them so they take the least amount of bag space? e.g. instead of having (3, 3, 3) stacks of an item that can stack to 5, have (5, 4) stacks instead

Items generally stack optimally unless you've manually intervened by splitting them.

Would it be possible to add the button back just so it guarantee all partial stacks are properly merged ? No need for sorting.

I noticed after being given through trade partial cloth stacks that they don't efficiently merge.