[General Topics] Fluora:
The Blackview BV9800 Pro is a relatively rare device, and has no support from LineageOS or any other popular ROM project I can find. This is kind of a shame, because it's a pretty cool device - in particular, it has an integrated thermal camera, and is also just a nice ruggedized phone at a surprisingly low price. The bootloader is unlockable out of the box without any need for an unlock code or other nonsense from the vendor, which is also a big bonus.

Being a Project Treble-compatible device, it's possible to run unofficial GSI builds of LineageOS on it, such as these, which are replacement images to flash over /system. These work well with the majority of the BV9800 Pro's functions (wireless, visible-light cameras, sensors, etc.), but getting the thermal camera to work requires a little bit more work. I have done this successfully, so I wanted to share what I did in case anyone else finds themselves in the same situation.

I have only tested these procedures on a BV9800 Pro (EEA version), running LineageOS 16 (Android 9) from the link above. Other versions of Android may work, but I do not know whether they do or not, and decided to stay with Android 9, since this is what the vendor ships on the device. Your results may vary if you decide to try a newer version.

The factory MyFLIR app for the device can be found at this location in the stock ROM:

/system/app/myflir-bv2.3.6-release-signed/myflir-bv2.3.6-release-signed.apk

However, if you try to just install it like a normal app package under LineageOS, it crashes on startup without providing any useful information. The system logs reveal that it crashes because it's trying to communicate with a system service that manages the thermal camera, but this service isn't installed. Fortunately, you can install it by just copying a few files from the factory ROM over to the LineageOS system. The files in question are located at these paths in the factory ROM:

/system/bin/leptonServer
/system/etc/init/LeptonCameraServer.rc
/system/lib64/libleptoncamera.so

If you copy these files to the same paths in the LineageOS /system tree, then the Lepton camera server backend, which is required for the MyFLIR app to function, will be installed and configured to start at boot.

SELinux seems to prevent the app from connecting to the Lepton server on my device, so I had to disable it by running

setenforce 0

in a root shell on the device. I didn't install it as a system app, though, which could be part of the problem. I don't know much about how SELinux actually works, but I feel comfortable enough disabling it. If you don't want to disable it, you can probably find information about how to make it allow the FLIR app to work, but I'm afraid I can't be of much help there.

You can find a copy of the stock BV9800 Pro ROM here on the Blackview forum.

If you want to root the stock ROM to allow you to inspect /system, this thread explains how. If you prefer, you can instead extract the ROM zip archive on a computer, decompress the included system.img with simg2img, and mount it to inspect the contents directly, which is what I did. Modifying /system on a running device can be difficult these days, so it will probably work best to mount up the GSI image the same way and copy the files into it, rather than try to edit it in-place on a running device.

I hope this information helps. The thermal camera is one of the most important (and expensive) features of the BV9800 Pro, and getting it working was pretty much the deciding factor for me as to whether I would keep the (kind of bad) factory ROM, or get to enjoy all the perks of LineageOS. I'm not really knowledgeable enough to write a complete and trustworthy guide to installing LineageOS, though, so if you're just getting started, you'll want to find a more detailed tutorial about how installing custom ROMs (especially GSI/Treble builds) works.