There is a file on location: /home/lukas/dotfiles/zsh_plugins.txt and a symlink to it from ~/.zsh_plugins.txt.

Lets break down the path segments:

realpath ~/.zsh_plugins.txt
# -> /home/lukas/dotfiles/zsh_plugins.txt

realpath --relative-to=$HOME ~/.zsh_plugins.txt
# -> dotfiles/zsh_plugins.txt

dirname $(realpath --relative-to=$HOME ~/.zsh_plugins.txt)
# -> dotfiles

basename $(realpath ~/.zsh_plugins.txt)
# -> zsh_plugins.txt

basename --suffix ".txt" $(realpath ~/.zsh_plugins.txt)
# -> zsh_plugins