Not a dumb question at all! The launcher doesn’t make it easy to figure out which OS version you’re running, unfortunately. But I think this post might help:
On the Settings->About screen, near the bottom it will show the Kernel version. There’s more related information in that thread.
I guess I misspoke that Retroarch never works and always has a black screen, it’s just that it happens so frequently, I gave up on it in OS 3. When and if it does work (and doesn’t later lock up), it runs great with no screen tearing. I’ve seen reports on the forums about OS 2.1 having screen tearing issues, although it does seem to consistently work. The OS itself has battery drain issues though and sounds like it runs the device hotter than it should.
I got my device mainly as a “real” device for Pico-8, and to tinker around with porting other games, etc. The emulation was a big draw too, but I’ve kind of learned to live without it (still sad about that though), because the current OS runs everything else so much better. I wish they’d fix the Lima display drivers though, because it would be an excellent device if it had the same performance as the current OS, but could also run Retroarch and emulators reliably. I haven’t completely given up hope, but there have been lots of discussions (and complaints) on the forums here and very little response or indication that a new version of the OS is coming, or when it might be released. Even a quick tutorial of how to build a new version of the OS with updated/working drivers would be helpful, though I guess it could cause some chaos if there were lots of random user builds floating around on the forums.
In any case, I’ve resigned myself to only using it for Pico-8 and some other random stuff. The standalone PCSX ReARMed (available somewhere in these forums, but I didn’t grab a link, sorry) for Playstation emulation works great on the latest OS, with excellent battery life and full speed performance. There’s a stand alone Genesis emulator available too that works great too. Most of the rest are covered by Retroarch (including the systems built into the launcher), which is annoying in this case since they are unreliable now, if they work at all. 
I ran with the 2.1 OS when I first got my device and liked it for emulation, but performance was poor and battery life was also poor since there wasn’t much optimization. In the latest OS things are optimized and it’s a great device… except for most emulation. I’m still holding out hope for a fix one day.