I managed to get UHD discs to work with my ASUS SBW-06D2X-U (LG) /w MT1959 rev.A102🎈
There's a lot of links and a lot of information, and so my first attempt to get this working failed.⛈️
For others also asking about this drive, what seemed to work was the following:📖
I downloaded and unzipped the firmware + patcher here. In the folder were two BU40N firmwares files and a patcher application:
https://drive.google.com/file/d/102V7DU ... sp=sharing
I flashed my drive with the application. First with the DE_LG BU40N_1.00.bin, and then with the DE_flash_HL-DT-ST_BD-RE_BU40N_BU10.bin
I have zero idea if that's correct, but in my mind the goal is to "downgrade" to the 1.00 version, and then upgrade to a newer patched version.
I got no errors, but the completion message was also not exactly confirming clear success either.
Next, I loaded up SDFtool Flasher, which I found here (viewtopic.php?f=16&t=22896), and then flashed the v1.03 firmware of the BU40N that I found here (https://drive.google.com/file/d/1HRnbXi ... 0FCdM/view - "the all you need firmware") Comparing dates on the downgrade firmware I used earlier, and this all-you-need v1.03 one, it seems that the 'all-you-need' one was a few days fresher (April 27 vs 23 2019). For added reference, the v1.00 downgrade firmware is marked Feb 5, 2019, so a bit older still. I think I have the newest firmware installed now, but I'd imagine that this step is not needed? I just really wanted to confirm that SDFtool would work, and it did.

Earlier on in my attempts to get this working, I had already tried using SDFtool Flasher to flash the BU40N file (from the "all you need firmware" package), but it failed. I guess the secret was to downgrade first with the other flasher, using the older 1.00 firmware first. This part tripped me up I think and my fears of bricking my device kept me from moving forward at the time. Slim vs external; LG vs Asus, old vs new; MK vs DE, etc - I was a bit lost initially.
After flashing successfully with SDFtool, I restarted the drive and my UHD movie (the Joker) started loading! Previously it couldn't read the disc at all. I bought the Joker simply to try to get this all working, as I don't really watch or own Bluray movies, but it's great knowing I now can. I'm keen to get into learning more about MakeMKV now and how to rip discs; looks fun.
As a side note, I struggled to get just FHD Bluray discs to play initially, while taking a break from UHD, but VLC required download key files to get things working; I couldn't figure it out honestly. I found out that there is a hidden free version of PowerDVD called "essentials" that plays 1080p Blurays effortlessly; it lacks ripping and 4K support, but that's what MakeMKV offers. [update!! Turns out MakeMKV has a VLC integration and makes it super easy to use VLC for Blurays also. doh! I just found that out!!]
Another side note, the ASUS SBW-06D2X-U is very picky over power. I had to use a high quality USB charger to provide enough power to get it to work reliably; I tried some other chargers / USB 3.0 ports and it failed with them. It would try to spin up, but then fail to actually read. I can imagine there have been quite a few product returns due to this issue.
Anyways, I hope that this helps someone who was new to this all