Time and time again on this forum I witness members advocating for the dash cam technologies, capabilities and features that are not only highly impractical but also unwise even if they were to become available. Such things as 2.7K, 4K and H.265 compression are typical examples.
This comes about because for the vast majority of members here on DCT, the concept of recording video for evidentiary purposes is entirely theoretical. Only a tiny percentage of members here have even been in a situation where they have been required to submit video evidence in an serious legal case or significant insurance matter. In fact, many members seem more interested in dash cam video (bad driving / crash footage, etc.) as a form of entertainment, with sousveillance evidence only as an afterthought should they happen to need it. The problem with ultra high resolution video is that most people don't stop to think about what happens with your footage after it leaves your hands.
I first became interested in dash cams because of an ongoing criminal harassment matter that involved numerous submissions of video to law enforcement. I learned first hand how vital it is that you hand off video (including and especially the all important raw footage you may be required to supply as evidence) that it is as absolutely easy and idiot proof for anyone in the evidentiary chain of custody to view. You often won't get a second chance if they can't. If say, a clueless insurance adjuster or some low level ADA in a prosecutor's office runs into too much trouble attempting to view your 2K or 4K footage on their out-of-date computer, they'll move on to the next case. For this reason, I have become a strong advocate for the requirement that a good dash cam needs to be able to record high quality native 1080p footage.
Many, many parties you may have to hand off 2K or 4K footage to, such as law enforcement, prosecutors, attorneys, courts of law, insurance company personnel and other random bureaucrats more often than not have to rely on older computers and older software that won't properly play 2K or 4K (or H.265) video. Many of these folks wouldn't even know what you are talking about if you mentioned the term "2K" or "4K"!
My practice nowadays is to record 1080 dash cam footage and nothing else unless it is an ancillary camera in support of a primary camera.
Put aside the question of whether 4K dash cams are technically viable at this point in time and think about what you may need to actually do with the footage you shoot. Forget about 2K and 4K video until such time as these resolutions become ubiquitous the way 1080p is now. Until such time, the best course of action is to use a camera that provides you with the highest quality 1080P results.