The Paper version only works on Paper, it will not work on Spigot or Bukkit
If you use the Paper version and a plugin does something with the player's name or id during player prelogin event, it will break on Paper 1.15.2 build 355 or lower. Uses build 336 or higher to avoid this issue.
Lucky Perms is an example of a plugin that does read the player's name and UUID during player prelogin so you will not be able to login on 1.15.2 build 355 or lower.
If these releases break, I will not be updating them unless I need it for my own reasons
The Fabric version was built for MC 1.14.4 but was tested and still works on 1.15.2.
The Paper version was built for MC 1.15.2, the latest version at the time of publishing. If it breaks on 1.16 and I am still working on my plugin, I may update this.