Both sentences are very similar, and mean almost the same thing. In spoken language, you could use them interchangeably and any native speaker would understand you just fine. However, they do have some subtle differences that give the sentences a bit of a different meaning. If you're focusing on written English, it may be important to keep these in mind as it would give a different flavor to your writing.

These kinds of questions are very common (I think this is the third one I've answered on this very forum). The difference is difficult to explain in plain English because it's just something that you kind of feel as a speaker. In my opinion, the best way to look at these questions is to view them from an analytical perspective. By breaking it down and putting the pieces back together, we can better understand the underlying meaning of why these sentences are different.

In the first sentence, the root is we usually do work (I'm removing our here because it's not relevant from a grammatical perspective). This means that the work is usually done. Do not (or don't) is an adjective phrase which modifies usually by inverting its meaning. So instead of meaning that the work is almost always done, it means that the work is seldom done.

In the second sentence, the root is we do not do work. Usually is an adjective that modifies do not, meaning that most of the time, the work is not done.

Looking at it from this perspective, try to see if you can understand what's going on here and why the sentences are different. Good luck!