A few facts:
older-generation WOLEDs likethe C6 only supported 60Hz refresh, did not support BFI, and had no issues with flashing/overshoot.
In 2018, LG introduced 120Hz refresh (only suppored through USB), introduced 50% BFI@60Hz, and late in the model year, the issue of flashing/overshoot was discovered.
LGDs development cycle for the 2019 WOLED panels was largely complete by the time the flashing/overshoot issue materialized (LGE needs final panel no later than mid--year to be ready with pre-production product prototypes by CES).
CES 2019 saw several impressive new features including 120Hz refresh now supported through HDMI2.1 as well as advanced 120Hz BFI (50%), different BFI levels @ 60Hz (25%, 50%, 75%), and 3.5ms MPRT. This capability was done, it was working, and it was even included in the review samples that were sent out just prior to release (was John Archer reporting on one of these review samples or final prouction FW?).
The FW 'fix' for the flashing/overshoot problem on the C8 was released around this time - after CES and before C9 launch and availability.
Also in this period after CES and before production release, we heard the first report from Germany that the 120Hz BFI features did not make it into the final product.
I believe the pre-production review samples were sent out after that report from Germany, so we were relieved to hear from first reviewers of the C9 review samples that the 120Hz BFI functionality was present (and appeared to perform splendidly).
Then when first C9 product samples reached early retailers like Value Electronics, we heard from jrref and others that the production FW no longer supported the 120Hz BFI features.
That's now been confirmed directly by LG and through other official 'launch' events like the one in the UK - 100/120Hz BFI features have been 'abandoned' on the 2019 WOLEDs.
And finally, we're seeing that in addition to the 2019 WOLEDs having identical BFI finctionality to the 2018 WOLEDs, the flashing/overshoot 'fix' that was released on the new C8 FW apparently addresses the flashing/overshoot problem in an identical manner to it's continued presence on the C9 (meaning the problem has been greatly reduced, but not eliminated).
Part of the flashing/overshoot 'fix' implemented in the new C8 FW appears to involve temporal ditherng, and using half of the 240Hz Effective Refresh Rate refresh cycles for temporal dithering to reduce the flashibg/overshoot problem means those same refresh cycles are not available for the insertion of black frames at 120Hz.
So the overwhelming liklihood of all of this is that the hardware cause of the flashing/overshoot problem exists on the 2019 WOLED panels identically to how it exists on the 2018 WOLED panels and LG learned of the problem too late to make any changes in hardware.
The FW 'fix' that was developed for the 2018 WOLEDs was the only option to reduce the underlying issue on the C9 prior to release (and to avoid a repeat of the embarassing 2018 uproar over this defect).
This FW 'fix' was finalized following completion of C9 development but before production release and the need to include it on the C9 production release (at the expense of 120Hz BFI) was made at the 11th hour to avoid an even larger launch fiasco.
The net-net of all this is that in the areas of BFI as well as flashing/overshoot, the C9 is identical to the C8 (and probably always will be).
If we see a repeat of these issues and limitations on the 2020 WOLEDs, it will mean it is something fundamental to the technology (or at least LGD's implementation of it).
If we see 120Hz BFI implemented on 2020 WOLEDs along with a complete elimination of the flashing/overshoot issue, it will mean LGD just needed a full WOLED panel product cycle (meaning at least 18 months prior to LGE product launch) to eliminate the issue in hardware.
The C9 appears to be a significant upgrade from the C8, especially in the area of near-black performance, but my guess is that anyone counting on ever getting 120Hz BFI on a C9 (or complete elimination of the flashing/overshoot issue) is probably in for dissapiintment...