@jollysea hold on, I have some stuff for you.
I'll edit this post once I have it.

Edit:

This might be useful
https://github.com/dylanaraps/pure-bash-bible

I got it from this video (the channel has other interesting video around the topic)
https://www.youtube.com/watch?v=Jllnhid7O7w

One liners are good way to learn about commands and way to do things
https://www.bashoneliners.com/oneliners/newest/

I've not use it, but code golf can be a fun way to learn, here is some tips to use code.golf with bash
https://code.golf/wiki/langs/bash

On the more boring side of bash (permision etc), there is a ton of good material for the RHCE or now RHCSA exam, some will cover bash, builts in etc.:
https://www.redhat.com/en/services/certification/rhcsa