[LG V30 Questions & Answers] TheDannemand:
Thank you for pointing that out, [MENTION=3250376]ChazzMatt[/MENTION]!

[MENTION=8517348]CuDem[/MENTION]: ChazzMatt is completely right. I forgot you have to use Download Mode to roll back to 20b in order to use the WTF bootloader unlock trick. Duh... So that's not a path for you to fix this.

To me it sounds like this phone WAS previously BL unlocked and rooted, and that's where the problems with Download Mode began. Or LOS-17 was installed, causing the Camera and Fingerprint issues mentioned. Maybe the previous owner re-locked the bootloader and sold the phone, pretending it was in better shape than it was?

I can think of the following:

1) If you know the history of the phone and that it was never unlocked or rooted before, then I would still say it is unlikely that its laf partition (which contains Download Mode) was actually corrupted. The phone could still have been Frankensteined incorrectly or "abused" with LGUP, but because of very thorough integrity checking when flashing through Download mode, it would rarely cause you to lose Download mode. So if you KNOW it has never been BL unlocked, I would continue trying on a different computer, with different cables, different USB ports, drivers etc. If fastboot devices returns a serial number, that's a good test that USB drivers and ADB connection is working. But you could still have LGUP issues. Again, some computers (particularly some AMD processors) are simply not compatible with LGUP.

2) See if you can find the OTA update file for US99830b and force update it using LGUP FOTA mode. This works with the phone booted into the OS and MTP (file sharing) turned on. It may not complete the update since you are already on 30b, but it will rewrite laf (Download mode) as its first step. Several H932 owners have done that back in the Oreo days, and a few have done it on Pie. Study the thread linked below for the background and the procedure. But DO NOT use the files shared in that thread, NOR ANY OTHER H932 FILES. You will brick your phone if you flash anything H932 on any other model, or vice versa.

[H932][T-MOBILE] URL for the H932 Pie OTA file

https://xdaforums.com/lg-v30/help/h932-url-h932-pie-ota-file-t3991417

3) Use Qualcomm 9008 mode and the leaked firehose to rewrite the laf partition (or the entire firmware). This is a more complex procedure, which I cannot help you with, but it allows writing almost anything to the phone, and should be compatible with all V30 models EXCEPT H932. See the thread linked below, and be ready for some hard work:

LG V30 Unbrick guide (Qualcomm EDL 9008 Mode, Hardbirck, with no download mode)

https://xdaforums.com/lg-v30/how-to/lg-v30-unbrick-guide-qualcomm-edl-9008-t4048661

4) Contact the XDA member from Moldova who can repair your V30 remotely for a fee. His name always escapes me, but maybe Chazz or others remember. He is also on eBay:

Remote Service Repair Unbrick LG G7 G6 V30 V35 V40 in Qualcomm Mode 9008

https://www.ebay.com/itm/Remote-Ser...794311?hash=item46994ee187:g:gd0AAOSw0qFdJi7a

And that's all I can think of. Once again, please report the outcome back here, as it may help others. Good luck to you :)

Edit: Oh, and then there is Update Error Recovery on the Update tab in LG Bridge, which has worked for some to fix Download mode. It also runs from inside the OS (at least initially). But I am not sure LG Bridge works with US998, let alone on Frankenstein'ed phones. Still, it's easy, so worth a try.