"Traveling alone is a great way to get in touch with yourself." On alternate Earths, you will often find other versions of the Dark Knight. These include a vampire Batman (inspired by the comics story Batman & Dracula: Red Rain), a pirate-themed Batman (Captain Leatherwing, based on Detective...
braveandbold.fandom.com
In theory, Batman: The Brave and the Bold, DC Animated Universe, Superfriends, The Batman and Scooby-Doo would be canon. Supernatural doesn't count, that episode was a remix of a previous episode except with Supernatural characters inserted into the story.
Will I include this?
Well, I guess I'd have to binge DC Animated Universe and the Watchtower Database, Keeping note of every date mentioned, and read every comic tie in and the hundreds of books, watch every Scooby-Doo episode, Batman: The Brave and the Bold, Superfriends and The Batman. Then I'd have to consider things with similar animation styles. Is Superman: Brainiac Attacks in the multiverse? Is Gods and Monsters? Then I'd have to consider whether the The Dark Knight Returns Batman is an alternate version or the animated version, possibly adding Batman: Year One, DC Showcase: Catwoman and Batman: The Dark Knight Returns: Deluxe.
I think it's fairly clear what is canon and what's not for now. If you want to count this one second cameo, awesome.