I'm working on an amateur-to-pro photo processing app, and can't figure out the best way to direct first-time users/installs to their relevant feature sets. Anyone have good examples of this onboarding for desktop apps?
Have a look through here: http://www.useronboard.com/onboarding-teardowns/
Most general recommendations and inspirational overviews are focused on web applications and mobile applications for consumer domains. Very few are touching upon business applications or extended/expert-use applications like the one you mention here, or the ones I am designing too. And here I am making a distinction between actual desktops applications that run in the OS, as opposed to desktop-sized application that run inside a desktop web browser. These are very different, although the goal of the latter is sometimes to mimic the first.
There really are not that many good examples out there as far as I have found. I would be very interested in seeing them too :-).
Most desktop applications expose more or less all their features from start, so progressive disclosure might not work as well as in a web-based app. Also, there is often no log-on and set up user account process that needs to be done, so a guided "learn-while-you-build" tour is also not really an option.
So what to navigate after?
Starting from macOS Human Interface Guidelines' general statement that designers should "Think twice" before providing an onboarding experience to new users: https://developer.apple.com/library/content/documentation/UserExperience/Conceptual/OSXHIGuidelines/StartStop.html , the goal should be to design your initial screen(s) similar to other well-known UI, so that any user would know what to do in the first few steps.
And then we as designers and developers should try to understand the first few basic actions that our users might take, and make sure that these actions are found in the first empty-state or introductory screen.
I like how Adobe is doing this in their different applications: Photoshop recently changed their onboarding dialog to a empty-state screen with a selection of actions like New or Open, and a list of most recent files the user had been working on.
This theme varies in other Adobe products, and I think the most extreme is Adobe Character Animation where the new user is actually taken through a story-telling that introduces the basic (and some advanced) features.
I don't know if these comments help any, but I am very interested in hearing your and other people's findings in this area also.