There are two answers here
If we are talking about the current DC Universe
After Dark Nights: Death Metal, the DC Universe goes into a possible future, with the “Future State”, then to the Infinite Frontier
The Dark Night Dearh Metal series
Rebooted the DC Universe
So that everything in the more than 80 year old history of the DC Universe actually happened.
Before the heroes and villains didn’t remember everything
But that series would be very confusing to a new reader
But
The Dark Night Death Metal 7
pages 26 to 36
Infinite Frontier 0
Might be enough
Here are the major
Starting points since that series ended
Justice League 2018 59
Wonder Woman 2016 770
The Flash 2016 768
Green Lantern 2021 1
Action Comics 2016 1029
Batman 2016 ( Tynion starts at 86 (maybe 101 is new start))
Detective 2016 1035
Batman Urban Legends 2021 1
Joker 2021 1
Catwoman 2018 25
Swamp Thing 2021 1
Harley Quinn 2021 1
Nightwing 2016 78
Suicide Squad 2021 1
Teen Titans Academy 2021 1
Wonder Girl 2021 1
Superman Son of Kal el 1
Batgirls 1
If you are talking about understanding the entire Comic Book Library here
First
Watch
Secret Origins the Story of DC Comics
In that hour and a half you will get a good overview of most of our comic book library. It was filmed in 2009 so of course can’t talk about newer than that
This is my complete list for New DC Readers. It is intended to introduce most of the major characters of the universe at a basic level. It is by year
This is my
Batman for new readers