Hello. is this still being worked on? thank you for answer.

It has never been worked on. It's a very complex topic.

Since OpenMPT has separate undo buffers for all the things you can edit (patterns, samples and instruments), its undo implementation and behaviour is very different from other applications: It makes sense that when you are e.g. in the sample editor, pressing Ctrl+Z will always undo the last change you did to that sample, even if the last action you actually carried out was maybe something in the pattern editor. However, this also makes it a lot more complicated to come up with a sane behaviour for the order list undo: There are many undo/redo actions that would have to support undoing both pattern and order list changes at the same time. For this reason, it would probably make sense to unify the order list and pattern editor undo buffer into a single buffer. But on the other hand, I think that sometimes could also be very annoying to the user, they might want to undo something in the pattern but instead they will undo something in the order list without noticing. Since I never came up with a clear answer which of the two behaviours would be more acceptable, I didn't even start implementing either of them.