I was not familiar with this term and had to look it up. From my brief search, it also seems like snake oil, and I don't know why someone would not go to a real physical therapist instead.

DO are real doctors. Rarer than MDs because there are less schools but totally real docs. My Mom with 30 years nursing experience says their training is basically identical, but DOs are generally nicer.

It depends on the country. Everywhere but the US, I believe, osteopaths are witch doctors on the same level as chiropractors. In the US, they were originally like that, but their professional organization basically pushed it into being a real medical degree.

Now they go to the same length schooling as MD's, and take the same exams as far as I know.

The core of the whole discipline, osteopathy, is a pseudoscience, though. While they are usually competent doctors they still have that core of pseudoscience. They like to market themselves as more "holistic", but that's usually a good dogwhistle term to let you know information not supported by science is going to follow. They bring up that they are the same as MDs, but with additional training in osteopathy, but that can't be true because the schooling is the same length, so to fit in the pseudoscience, they get less science.

The real reason why we have DO's is that we don't have capacity in our country to educate enough MDs, so we have this weird parallel system.