I like mkcd! I have the same thing. Although what I use more is a function I pair with it that specifically creates a temporary directory, and cds to it. It's useful for temporary work, like extracting from a zip file.

These are my Nushell implementations:

# Create a directory, and immediately cd into it.
# The --env flag propagates the PWD environment variable to the caller, which is
# necessary to make the directory change stick.
def --env dir [dirname: string] {
  mkdir $dirname
  cd $dirname
}

# Create a temporary directory, and cd into it.
def --env tmp [
  dirname?: string # the name of the directory - if omitted the directory is named randomly
] {
  if ($dirname != null) {
    dir $"/tmp/($dirname)"
  } else {
    cd (mktemp -d)
  }
}