schlosrat

I have good news for you! First, you can move the folder out of the Steam folder, and you can launch it directly if you happen to want to do that. Thus, it's possible to buy it on Steam and use it just like it's a direct Download. I moved mine from "C:\Program Files (x86)\Steam\steam\steamapps" to "C:\Kerbal Space Program 2", then put a shortcut to "KSP2_x64.exe" on my desktop. Works like a charm!
More good news! The files you're looking for are not in the Steam folder, they're in your user's AppData folder! Navigate to "C:\Users\<your Windows User Name>\AppData\LocalLow\Intercept Games\Kerbal Space Program 2\Saves\SinglePlayer\<Your Campaign Name>"
Under this folder you'll find craft files (they're sets of *.json, *.meta, and *.jpg files now), but you'll need to dive one level lower into the "Workspaces" within your campaign, as KSP2 now treats the things you're creating as whole workspaces and not just one craft. This is part of how they make Merge work I think.
Also, and just as a bonus, if you head over to "C:\Users\<your Windows User Name>\AppData\LocalLow\Intercept Games\Kerbal Space Program 2\Global" you'll find a "PhysicsSettings.json" file. Edit this with any text editor (make a back up first, of course!) and you can stiffen up your wobbly rockets a bit by boosting the value for "JOINT_RIGIDITY". The default is 1500. Try 1500000 and see if that helps.