It was interesting to me the author seems to use 'old-school' Clojure, for lack of a better phrase, with lein as the build tool, etc., rather than more recent tools/stacks; I don't use Clojure myself, is my impression off?
deps is more flexible, but I you just want to run a repl, build and deploy code then lein still works fine.
I usually default to leiningen: I can't be arsed to spend time configuring deps to do what lein does out of the box. (For example: building an uberjar)
I was lost when I moved to deps from lein, but just forking and cloning https://github.com/practicalli/clojure-deps-edn as $HOME/.clojure solved the problem - this base deps.edn contained all the aliases I needed - creating a new project, searching and adding dependencies, hooking up data inspectors like portal or reveal, testing, code coverage, benchmarking, building uberjar etc. Moving to deps also introduced me to polylith [1], which has been very useful for building large multi-component projects