Python is one of the worst offenders here. I don't think Python's poor behaviour should excuse Lua's.

But I can also see why Python is making breaking changes - a lot of Python is so bad it really makes sense to clean it up. I dunno if Lua is in that situation.

Anyway I think I would look to other languages like Go, Rust, Java, C++ which do a much better job. I don't think Go or Rust have any backwards incompatibilities (at least very very few) and C++ has a small number but they're for stuff that is truly ancient or almost completely unused. It's totally possible if you care about it.