As the object_name_linter already does, class suffixes for S3 generics shouldn't be part of the linted symbol.
That is, object_length_linter(30) (the default) shouldn't lint this example:

my_generic_function <- function(x, ...) {
  UseMethod("my_generic_function")
}

my_generic_function.my_cool_class <- function(x, ...) {
  cat("How cool and generic!\n")
}