DC Comics is as known for their exploration of alternate realities through imprints like Black Label and Elseworlds. However, many stories that fans have written off as a one-off, out of canon tales have slowly seeped into continuity. While some of these stories have become an official part of main canon, others were stealthily told as extensions of alternate dimension tales.
Source:https://www.cbr.com/dc-comics-canon-ranked/