Obviously not all the films are connected, but there’s still a way to watch them that has a flow and connects similar story beats.
This is my totally unofficial “canon” watch order.

ORIGINS:

Batman: Year One

Batman: Gotham Knight

Wonder Woman (2009)

Green Lantern: First Flight

Green Lantern: Emerald Knights

Superman: Doomsday

Superman VS The Elite

DC Showcase: Superman / Shazam!: The Return of Black Adam* *(a collection of shorts that also features The Specter, Green Arrow, and Jonah Hex)

Superman / Batman: Public Enemies

Superman / Batman: Apocalypse

Superman: Unbound

Batman: Under the Red Hood

Batman: Death in the Family

Justice League: Crisis on Two Earths

Justice League: Doom

THE DC ANIMATED MOVIE UNIVERSE:

Justice League: Flashpoint Paradox

Justice League: War

Son of Batman

Justice League: Throne of Atlantis

Batman vs. Robin

Batman: Bad Blood

Justice League vs. Teen Titans

Justice League Dark

Teen Titans: The Judas Contract

Suicide Squad: Hell to Pay

The Death of Superman

Constantine: City of Demons

Reign of the Supermen

Batman: Hush

Wonder Woman: Bloodlines

Justice League Dark: Apokolips War

Constantine: House of Mystery

THE TOMORROWVESE

Superman: Man of Tomorrow

Justice Society: World War II

Batman: The Long Halloween

Green Lantern: Beware My Power

Legion of Super-Heroes

Justice League: Warworld

Justice League: Crisis on Infinite Earths (trilogy)

ANIMATED ELSEWORLDS

All Star Superman

Superman: Red Son

The Batman vs. Dracula

Batman: Gotham by Gaslight

Batman: The Doom That Came to Gotham

Batman: Ninja

Batman Vs the Teenage Mutant Ninja Turtles

Deathstroke: Knights & Dragons

Batman: Soul of the Dragon

Catwoman: Hunted

Batman: The Caped Crusader

Batman Vs Two-Face

Batman: The Killing Joke

Batman: The Dark Knight Returns

Justice League: The New Frontier

Justice League Vs The Fatal Five

Justice League: Gods and Monsters

Injustice

Teen Titans: Trouble in Tokyo

Teen Titans Go! To the Movies

Teen Titans Go! vs. Teen Titans

Batman and Superman: Battle of the Super Sons

THE DCAU (AKA: THE DINIVERSE)

Batman: Mask of the Phantasm

Batman & Mr. Freeze: SubZero

The Batman / Superman Movie

Superman: Brainiac Attacks

Batman: Mystery of the Batwoman

Batman and Harley Quinn

Batman Beyond: Return of the Joker

ARKHAMVERSE:

Batman: Arkham Origins

Batman: Assault on Arkham

Batman: Arkham Asylum

Batman: Arkham City

Batman: Arkham Knight

Almost all of these films are streaming on MAX.