So I have tried installing lua with apt: sudo apt install lua5.3, the binary gets installed in /usr/bin (while the installation building from source had it insgtalled in /usr/local/bin): no news, darktable still won’t find the damned binary.
And to reply to @darix no I don’t think dartable looks for liblua, it actually searches for one of the following binaries: LUA53 lua53 lua5.3 lua-5.3 lua (as I can see in darktable/cmake/modules/FindLua53.cmake).
Anyway I’ve solved the issue following @wpferguson suggestion, i.e. I edited CMakeLists.txt file and enabled the internal lua interpreter by changing to ON this option:
option(USE_LUA "Build lua scripting support" ON)
(I know you guys know it already but I thought to leave a trace for somebody else that may have similar problems in the future).
Now I’m back with LUA support, thanks!