You can view the 6.0.0 milestone on GitHub for more details.
Remove --diff option (See also #1389, #1720).
--diff
Produce an error when invalid codes are specified in configuration (See also #1689, #1713).
Produce an error if the file specified in --extend-config does not exist (See also #1729, #1732).
--extend-config
Remove optparse compatibility support (See also #1739).
optparse
pycodestyle has been updated to >= 2.10.0, < 2.11.0 (See also #1746).
Pyflakes has been updated to >= 3.0.0, < 3.1.0 (See also #1748).
Require python >= 3.8.1 (See also #1633, #1741).
List available formatters in for --format option in --help (See also #223, #1624).
--format
--help
Improve multiprocessing performance (See also #1723).
Enable multiprocessing on non-fork platforms (See also #1723).
Ensure results are sorted when discovered from files (See also #1670, #1726).