Linux is not yet supported. There's a lot of requests for Linux support, and I am an experienced Linux developer. I want to get version 5.1 out before I start adding another platform.
In most cases, since your game code has its own dedicated thread to run, C++ and Lua games will run at the same speed. However if you are running a game with very demanding code, like something with hundreds of enemies, the executation speed of Lua would probably start to be to slow.
By default, C++ projects are set up to use C++17. I tried changing the languiage setting in Vidual Studio to "C++23 preview" and added the macro _SILENCE_ALL_CXX20_DEPRECATION_WARNINGS, and my Leadwerks game compiled and ran with no apparent issues.