Using information from WordPress.org, specifically the Releases page and History page, below is the release history of WordPress. Part of being a member includes site updates, including the core and plugins from the WordPress Plugin Repository, along with any premium plugins you maintain membership for receiving updates. While this provides some history for WordPress, it's always advised to maintain your site's core at the latest release, the one still being actively maintained.
5.6 Branch
The 5.6 branch was named for Nina Simone and released December 08, 2020.
5.6
December 08, 2020
5.5 Branch
The 5.5 branch was named for Billy Eckstine and released August 11, 2020 with 3 security updates so far.
5.5.3
October 30, 2020
5.5.2
October 29, 2020
5.5.1
September 01, 2020
5.5
August 11, 2020
5.4 Branch
The 5.4 branch was named for Nat Adderley and released on March 31, 2020 with 4 security updates so far.
5.4.4
October 30, 2020
5.4.3
October 29, 2020
5.4.2
June 10, 2020
5.4.1
April 29, 2020
5.4
March 31, 2020