That is probably the last release of Lua 5.3. Bugs reported later are probably fixed in Lua 5.4.
Lua 5.3 was released on 12 Jan 2015. Its main new features are integers, bitwise operators, a basic utf-8 library, and support for both 64-bit and 32-bit platforms.
The current release is Lua 5.3.6, released on 25 Sep 2020. There will probaby be no further releases of Lua 5.3.