You can see the reasoning for avoiding PC Mode in the Changelog.
Basically it will raise the EOTF and Gamma, ruining the pre-calibration done by LG for the stock presets, along with killing the ALLM functionality and also disabling most Clarity options useful for movies (as Smooth Gradation, TruMotion etc). It will also introduce text fringing on Windows and in the end visual differences between 4:4:4 and even 4:2:2 and 4:2:0 are unnoticeable, so all these things to lose are not worth it.
About HDR games, yes: when they do not provide any Peak HDR Luminance control at all it's better to stick with DTM: On (I updated all my links in my Patreon to reflect that, including Jedi Survivor, along with adding G3 numbers for HGIG as well). Considering that almost half of all HDR games released in the last 6 years won't have HDR controls, I also recommend DTM as the primary "set it and forget it" option for gaming, even more so on G3.
On G3 specifically, in fact, DTM: On coupled with Filmmaker Mode (with just the Black Level set to 48 instead of 50) behaves much better than previous years: it will basically leave the image untouched, even during night scenes or very dark scenes, except for "boosting" the highlights in the picture giving them "punch" while not losing detail around them in a very similar way of properly setup HGIG. I really like it now.
FMM will also preserve the new "dynamic color boosting" of 2023 series which will preserve the very high luminance colors directly competing and even surpassing QD-OLEDs rendition (Game Mode won't have that, along with being 100 nits dimmer), so in the end it's just best to also game with FMM with DTM: On (and Black Level 48) + ALLM: On which will result in the same low input lag as Game Mode as well, making it completely useless now ;)
