Yup, I get "Killed: 9" on macOS (Big Sur) too. I actually had some kind of problem (I think) with the original invocation:

    $ bash -c './redbean.com -vv'
    W2021-02-26T02:06:29.162953:tool/net/redbean.c:1144:redbean:83621] setsockopt(server, IPPROTO_TCP, TCP_FASTOPEN, &yes, sizeof(yes)) → EINVAL/err=22/errno:22/GetLastError:0
    W--------------------000026:tool/net/redbean.c:1145:redbean:83621] setsockopt(server, IPPROTO_TCP, TCP_QUICKACK, &yes, sizeof(yes)) → ENOPROTOOPT/err=42/errno:42/GetLastError:0
    error:./redbean.com: check failed: 0xffffffffffffffff != 0xffffffffffffffff (48)
    6fffffffff70 0000004034cf UNKNOWN
    6fffffffff80 000000403225 UNKNOWN
    6fffffffffc0 0000004027f3 UNKNOWN
    6fffffffffe0 000000402a21 UNKNOWN
    7ffeefbff870 00000040227b UNKNOWN