8.4 is not even backwards compatible with perfectly working code written to target 8.x. It doesn't materially matter that the code is written in "5.2" style if

8.4 is not even backwards compatible with perfectly working code written to target 8.x. It doesn't materially matter that the code is written in "5.2" style if it was meant to run on only 8.x. Even that style point is arguable. The author uses Composer! And Laravel! And mostly does use namespaces, outside of a few useful helper functions that are reasonably global so they don't keep needing to import them or use namespace prefixes.