Currently, we use -b as a shortcut for --base64. However, this is incorrect, the behavior of -b was changed in GNU 9.4 according to https://github.com/coreutils/coreutils/blob/master/NEWS:

'cksum -b' no longer prints base64-encoded checksums.  Rather that
  short option is reserved to better support emulation of the standalone
  checksum utilities with cksum.

For most algorithms, -b is a shortcut for --binary.

Thanks to @Rudxain for pointing out this issue in #6187 (comment)