PR is what your side does, propaganda is what the other side does.

Let's look at the definitions first.

PR: the activity of providing the public with information about your organization so that people have a positive idea of the organization's work.

Propaganda: information, ideas, opinions, or images, often only giving one part of an argument, that are broadcast, published, or in some other way spread with the intention of influencing people's opinions.

Not much difference. Isn't necessarily a bad thing, though.

Imagine your daughter/your relative's daughter calling you and saying that she is considering going to a drug party with people she doesn't know very well. Would you care to tell her that it might be a ton of fun, if that means she might go there even after hearing your counter-arguments about how dangerous it is? Or would you only say whatever it takes to make her not go there because you are worried about her safety? Probably the latter. And that's straight up propaganda on a small scale. But it's done for the greater good. Even though there is a significant chance that if she'd go, she'd actually have a great time.

And during wartime, propaganda is pretty much mandatory. There is no way around it. You don't want your population to be demoralized. Even more so your soldiers. They need some things they can cheer about and they always need hope. If people fall into despair during such time it's very bad for them.

Let's take Ghost of Kyiv as an example. Even if mostly a myth, it wasn't really some harmful disimformation that lead to anything bad. It was a morale booster. And boosting morale of people on the right side of the conflict is ultimately a good thing.