Despite being a technologically superior game in many aspects, there are areas where GTA 5 didn't do much better than its predecessor, Grand Theft Auto 4. One of them is the police AI. While the former's cops are highly aggressive and trigger happy, the latter's go about their day-to-day and react to players' crimes in a more realistic manner.
An example of this was recently given by @GTASixInfo on X, who posted a video of a Liberty City cop in Grand Theft Auto 4 conducting a traffic stop on an NPC.
The NPC in the video above has been stopped for speeding. The LCPD officer searches through their car's trunk and then proceeds to ask the driver for some documents. Some might think of it as just another world event, but it helps in bringing life to the NPCs and making the in-game world seem more believable.
Reacting to this video, a Grand Theft Auto fan, @lukasofficial_, called it another example of something that needs to return in GTA 6, Rockstar Games' upcoming release.
The OP replied to this comment by stating that it would make the game feel so much more alive. Another reply to this comment presented an idea of players having the option to either comply or turn this into a chase.

In fact, there are many other comments from fans on this X post who lauded the 2008 title and want to see such GTA 4 features return in Grand Theft Auto 6.

What's interesting is that Grand Theft Auto 6's leaked development footage did suggest that its cops might behave in a more realistic manner as compared to Grand Theft Auto 5. @Injirleefe's comment on the X post in question also recalled seeing something similar in the leaks.
That being said, Grand Theft Auto 6 police mechanics are yet to be showcased officially as of this writing.
Grand Theft Auto Fans want GTA 4-like police mechanics to return in GTA 6

Many Grand Theft Auto fans seem to want Rockstar to implement cops in Grand Theft Auto 6, similar to what is present in Grand Theft Auto 4. As already stated, we haven't got an official look at Vice City and Leonida's police behavior yet, but the Grand Theft Auto 6 leaks did showcase some things.
For instance, a police dispatch timer was visible in a leaked clip wherein Lucia and her partner were robbing a diner. This suggests that cops could take a certain amount of time to reach the crime scene, instead of spawning instantly. The leaks also suggested the police may or may not always have a complete description of players' vehicles, which could be an interesting predicament.
Nevertheless, readers should note that things can change from development to the final release. So, it is best to wait for official information directly from Rockstar Games, which should arrive at some point leading up to the GTA 6 release date.