Created by Greg Berlanti, the Arrowverse started as one small Arrow/Flash universe, and has now become a franchise taking place on Earth-1. Shows like Supergirl and Black Lightning are not canon to the Arrow/Flash universe because they didn't originally air on the CW. After Crisis on Infinite Earths (note: this link leads to the comic), they both take place on Earth-Prime, but it's almost exactly like Earth-1 due to the Spectre.

Shows included in this post-Crisis Earth-Prime are:

• Arrow (2012-2020)
• Flash (2014-2023)
• Constantine (2014-2015)
• Vixen (2015-2016)
• Legends of Tomorrow (2015-2022)
• Batwoman (2019-2022)
• Supergirl (2015-2021)
• Freedom Fighters: The Ray (2017)
• Black Lightning (2018-2021)

Earth 2:

• Stargirl (2020-2022)

Earth 9:

• Titans (2018-2023)

Earth 19:

• Swamp Thing (2019)

Earth 21:

• Doom Patrol (2019-2023)

Earth-TUD25:

• Superman & Lois (2021-2024)

Notable Parallel Earths from Pre-Crisis:

• Earth-66 Batman (1965-1967)
• Earth-89 Batman (1989)
• Earth-90 The Flash (1990-1991)
• Earth-96 Superman Returns (2006)
• Earth-167 Smallville (2001-2011)
• Earth-203 Birds of Prey (2002-2003)
• Earth-666 Lucifer (2016-2021)