One sentence may contain both a maf'ul bihi and a maf'ul mutlaq.
ضَرَبَ السَّارِقَ ضَرْبًا شَدِيدًا
- Whom did he strike? السَّارِقَ — maf'ul bihi.
- What kind of striking? ضَرْبًا شَدِيدًا — maf'ul mutlaq with its description.
Both are mansub, so the final fathah alone cannot tell their roles. Meaning and the question each expression answers distinguish them.