Another example is Once Upon a Time in Hollywood (2019), where Brad Pitt was nominated for and won Best Supporting Actor, even though he played an equally important role to Best Actor nominee Leonardo DiCaprio.
ɐnˈʌðɚɹ ɛɡzˈæmpəl ɪz wˈʌns əpˌɑːn ɐ tˈaɪm ɪn hˈɑːliwˌʊd tˈuː θˈaʊzənd nˈaɪntiːn, wˌɛɹ bɹˈæd pˈɪt wʌz nˈɑːmᵻnˌeɪɾᵻd fɔːɹ ænd wˈʌn bˈɛst səpˈoːɹɾɪŋ ˈæktɚ, ˈiːvən ðˌoʊ hiː plˈeɪd ɐn ˈiːkwəli ɪmpˈoːɹtənt ɹˈoʊl tə bˈɛst ˈæktɚ nˈɑːmɪnˌiː liənˈɑːɹdoʊ dˈaɪ kˈæpɹɪˌoʊ.