It is also in Coreutils 8.22 in RHEL7.

https://man7.org/linux/man-pages/man1/dd.1.html

Edit: I just found this in the coreutils 9.0 changelog:

  dd now counts bytes instead of blocks if a block count ends in "B".
  For example, 'dd count=100KiB' now copies 100 KiB of data, not
  102,400 blocks of data.  The flags count_bytes, skip_bytes and
  seek_bytes are therefore obsolescent and are no longer documented,
  though they still work.