Have you checked if Panasonic Lumix GX9 has any specific compatibility requirements?

I've had Olympus M.Zuiko 25mm f/1.2 PRO on my Panasonic Lumix GX9 for since fall. It performs well, also worth noting perfect fit for Panasonic Lumix GX9. Does the job well.

Are you prioritizing price, quality, or features for your Panasonic Lumix GX9?

Got Olympus M.Zuiko 25mm f/1.2 PRO installed on my Panasonic Lumix GX9. I've found that, it has fast autofocus, another thing works seamlessly with Panasonic Lumix GX9. Can't really complain about anything.

Went ahead and got Olympus M.Zuiko 12-40mm f/2.8 PRO for my Panasonic Lumix GX9. Honestly, it has fast autofocus, another plus works great with Panasonic Lumix GX9. Couldn't be happier with it.

I went with Olympus M.Zuiko 45mm f/1.2 PRO for my Panasonic Lumix GX9 after. Personally, great value for the money. also easy to use with Panasonic Lumix GX9. No complaints so far.

What's most important to you - portability, performance, or price for Panasonic Lumix GX9?

Ok so, looking at what everyone said, there is a big range from high-end pro glass to the basic kit lens. Most of the suggestions so far are kinda bulky tho, and since the GX9 is so small, you might want something that balances better for long walks. I’m still kinda new to this, but here are a few other ideas I've seen people rave about for travel that wont weigh you down: * Panasonic Leica DG Summilux 15mm f/1.7 ASPH - This one is super popular because it’s small and has that "Leica look" for street photography.
* Lumix G Vario 14-140mm f/3.5-5.6 II ASPH POWER OIS - If you're gonna be hiking or dont wanna keep switching lenses, this is basically the ultimate do-it-all travel zoom.
* Panasonic Lumix G 20mm f/1.7 II ASPH - It’s a pancake lens, so it makes the whole setup really easy to carry in a jacket pocket. Does the weight of the lens matter much to you? Some of those pro lenses are pretty heavy for a whole day of sightseeing, tbh.