I personally think 2K@60FPS is the best choice, then 2K@30FPS, then 4K@30FPS, the reason is, lack of devices to watch real 4K even the recording is 4K, 4K display is currently and generally applied in TV.
An FHD (1080) monitor is perfectly good for watching 4K video, just zoom in when you want to see more detail.
Even with a 4K device, if you want to see all the detail from a normal viewing position, most people will have to either zoom in or get up and move uncomfortably close to the screen!
2k is better suited for dashcam use than 4k, not because of playback options but it's a better balance of space/results/operating temperature, 4k has overheating issues, poorer low light performance, higher data storage requirements
The data storage requirement depends on the bitrate, not the resolution, which is why some dashcam manufacturers get away with only 25Mbps for their 4K cameras, while others provide 30Mbps for 2K cameras! Use of bitrate is a tradeoff in quality between many aspects of image quality, such as frame rate, colour fidelity, resolution, pixelation, sharpness, temporal noise, etc..
In low light the 4K cameras still have the better resolution. They do tend to suffer more from noise and motion blur, but sometimes resolution is the more important of the three, the motion blur is only a problem when there is motion, and a bit of extra noise doesn't always destroy important detail even when it doesn't look nice. When stopped, a 4K dashcam should win on detail at any time there is reasonable lighting, and on a dark road at night with no headlights or streetlights, no dashcam works adequately well!
All cameras can overheat in a parked car at midday in midsummer. As long as they protect themselves, for example by shutting down, the amount of time a UHD camera is not fully functional is just a compromise to be made in return for double the detail of QHD or quadruple the detail of FHD for the rest of the year. People who live in hot places may want to make a different choice to those that live in cool places.
there is not a huge difference between a good 2K and 4K.
It is not a huge difference, just double the detail.
FHD (1080),
QHD (2K),
UHD (4K):