A little disclaimer here. Most of the pictures I've posted here were taken to test the camera out. All of them hand held to test the OSS lens, focus and low light quality. None of them are worth even keeping let alone publishing.I bought this camera with two functions in mind:1. Focus tracking - I'd like to be able to take pictures of birds in flight for example, without having to fight with the camera to get the focus right.2. Low light still photography - the native ISO range of 100 to 32000 was a big pull.I'd tried out the previous generation of Sony mirrorless cameras and was very impressed with the low light pictures I'd managed to capture.On the first point, I tried pointing the camera into the sky in the general direction of a bird maybe 20m away and clicking (no half press or delay of any sort), and was stunned by the result.(Picture 1: F5.6;135mm;1/160s;100ISO)The bird was in focus!I've managed some reasonably decent shots of ants crawling on vine bugs that would've taken more time to get the focus right than the ants were willing to stick around for - and this was with the kit lens (18-135) that isn't really touted as a macro lens at all.(Picture 2: F5.6;135mm;1/100s;100ISO)In other words, on the first requirement, the camera passed with flying colours. No fiddling around with the (electronic) focus ring as long as there's a bit of motion from the object it's supposed to focus on. If you half press, it tracks.On the second point, I tried taking some pictures of a park in the dark (with some bright backlight). I jacked the ISO up to 3200. Steady shot helped with the 1/6th of a second exposure, but the noise was much more than I'd anticipated, so I set a cap of 1000 ISO after this - there's no way I'd use pictures taken at anything higher than this with the noise that shows up.(Picture 3: F3.5;18mm;1/6s;3200ISO - I used Image Edge Desktop to convert the RAW to high quality jpeg here)I found the noise levels at 800 ISO to be tolerable - of course I had to adjust the exposure to compensate for the lower ISO to 1.3s.(Picture 4: F3.5;18mm;1.3s;800ISO - I used Image Edge Desktop to convert the RAW to high quality jpeg here)Not impressed with the high ISO picture quality. My ten year old entry level Canon manages about as well (in the Sony's defence, the Canon has a 10mp sensor). If I resample to the same size, the Sony is a little better, but for a decade in tech enhancements, I expected so much more.The software on the camera itself is fiddly - with a LOT of luck to photographers who use this camera, they'll improve the convoluted menu system - right now it's quite a mess. It's a pain to navigate through, and the touchscreen isn't an input option at all.The software off the camera (Imaging Edge Mobile) for Android is terrible. It's half baked, non-intuitive, and shouldn't have been released till they actually tried using it themselves. This app apparently replaces the PlayMemories app - I can't imagine how bad that was for them to replace it with the rubbish they're pushing now.The camera itself had issues connecting to my WiFi (it detects my networks just fine, but after fiddling through entering the password, gave me a "SSID not found" or some other such error 3 times before accepting it - it hasn't accepted it again since then). And remember, the keyboard is controlled through the dial - no touchscreen for you!If you DO get the WiFi to play well with your router, the next worry is the desktop app. My Mac couldn't find my camera on the network when it did connect (my router sees it).I thought I'd try connecting it to my phone (there's an ad-hoc network option for this), so used the Imaging Edge Mobile app and went through the routine of connecting the device to my phone with it - had the phone scan the QR code on the camera screen which said it had connected, but the phone didn't agree. I tried on my Nokia 7.2. The viewfinder streaming worked on a OnePlus7 and a Moto G 6, then briefly worked on my Nokia 7.2 and crashed.When I tried registering the device, the Sony site told me it wasn't in the database, not to worry and that I could get in touch with customer support to help me register it. When I got in touch with them, I was told I'd get an SMS with an email address to send details of the camera and invoice to. I didn't get this SMS, and asked about the registration on the next call, but got a bit sidetracked by the software issues.Essentially, I resigned myself to either plugging the camera into my computer with a USB cable or taking the card out of the camera and plugging it into the computer.I DID want the location to be recorded in the EXIF data, but that didn't work with any of the 3 Android devices I tried. I tried getting in touch with customer support by chat and phone, but they either sent me to articles talking about paring it through PlayMemories (which has been deprecated), or walked me through resetting the camera and facing the same issues all over again. Eventually, one support person directed me to take it to a service centre.This is where the experience fell apart completely - it's a camera, and while it's irritating that I can't get some of the features I wanted, I'm still relatively happy with its core functionality.I asked the Sony customer care person where the nearest service centre was, provided my location and he gave me the address and phone number for one close by. I (thankfully) called them before going, and was told that they don't have any engineers who'd be able to help with my camera. I was advised to take it to the "Head office" on Mathura Road, New Delhi. I asked for their number and was told that they were closed because of Covid, so I asked what to do and was told to try another service centre on the other side of the city. By this time, I was sort of fed up, and decided that if there was something wrong with the camera, I may as well just return it while I could and possibly try getting a camera from another company that supports their customers (Canon service has been good with me on the one occasion I've needed help with my camera).PS: The 6400 doesn't have the "hackability" of the older cameras (6500/6300). There don't seem to be any third party tools you can install on this to work through Sony's software issues or deficiencies.