[LowLevelMahn]

Tools: IDA Pro 5 (Freeware) is the last Freeware version able to handle DOS executeables (official available by the ScummVM devs https://www.scummvm.org/news/20180331/) - IDA Pro still supports DOS-stuff with latest release - but not the freeware

or Ghidra - but the DOS/16bit support is sometimes lacky - but the decompiler is builtin

here is a list of articles to read: https://forum.stunts.hu/index.php?topic=4287.0