Lua 5.3.6 is a bug-fix release of the main Lua 5.3 branch. There will probably be no further releases of Lua 5.3.
Changes between Lua 5.3.5 and 5.3.6:
Lua 5.4 is the newest branch and Lua 5.4.0 has been released on 29 Jun 2020.
Want to play with Lua? Just try GeeXLab. GeeXLab is a prototyping engine and Lua is the main programming language: https://www.geeks3d.com/geexlab/