gnus-group-sort-function

gnus-group-sort-function is a variable defined in `gnus-group.el'.
Its value is

gnus-group-sort-by-alphabet

• This variable may be risky if used as a file-local variable.

Documentation:
*Function used for sorting the group buffer.
This function will be called with group info entries as the arguments
for the groups to be sorted. Pre-made functions include
`gnus-group-sort-by-alphabet', `gnus-group-sort-by-real-name',
`gnus-group-sort-by-unread', `gnus-group-sort-by-level',
`gnus-group-sort-by-score', `gnus-group-sort-by-method',
`gnus-group-sort-by-server', and `gnus-group-sort-by-rank'.

This variable can also be a list of sorting functions. In that case,
the most significant sort function should be the last function in the
list.

You can customize this variable.