You asked
Olympus pen e pl9 vs panasonic lumix gx9?
Both are 2018 Micro Four Thirds cameras with in-body stabilisation and a 2x crop, so they take the same lenses. Any lens you buy for one will fit the other. For the sensor background, see the main sensor sizes.
I'd pick the Olympus PEN E-PL9 if you're a beginner who wants a light camera with a flip-down selfie screen and 4K video. It's the simpler choice.
I'd pick the Panasonic Lumix GX9 if you want a bit more resolution (20.3 megapixels against 16.1), a tilting viewfinder, and a rangefinder-style body you'll enjoy holding.
Whichever you choose, the Panasonic Leica DG 25mm f/1.4 II is a lovely first prime. It frames like a 50mm on full frame and suits portraits and everyday shooting.
Written by Claude from this site's pages.