If you're a near absolute beginner then Linux Journey is a good place to start.

https://doc.opensuse.org/documentation/leap/startup/book-startup_en.pdf

The best pdf imo

https://fr.linuxfromscratch.org/view/lfs-stable/

To know what the standard packages do

I would look for something interactive e.g LFS but in containers (or VM or WASM VM) with checkpoints with instructions, something risk free yet hands on.

Not for books.

If by chance you understand German this is an excellent beginner course: https://www.math.uni-bielefeld.de/~frettloe/teach/unix20.html otherwise I would grab a book; but I have no specific book to recommend. However, to name some I found interesting after a quick search:

• How Linux Works: What Every Super-User Should Know
• The Linux Command Line

https://www.linuxfromscratch.org/
here's latest generated document
https://www.linuxfromscratch.org/lfs/downloads/development/LFS-BOOK-r12.3-98-NOCHUNKS.html

What do you consider a structured approach? Are you after something with video lessons and lesson plans or do you just want to be thrown ideas about what to research?
If the latter, here's some ideas:

• What are kernel modules?
• How do kernel drivers and kernel modules differ?
• What are daemons in Linux?
• How to use crond?

Try your local library - one of the most underrated free resources.

Nearly every lib I've been to had at least a couple of decent linux books, so you can just snoop around and check out which ones you like.

The book that got me started was "friheden til at vælge Linux" (Freedom to choose Linux), at the time it was available in other languages, but I can only find the Danish version online:
https://linuxbog.dk/ (last updated in 2020)

When I started my LPIC I bought the "LPIC-1 in depth"., it's a bit dry but very thorough.

Highly recommend this wargame challenge from over the wire. It makes you think and also feels like hacking. Youre just using linux commands to find passwords but the skills transfer to heaps of usage across systems. It can be a little beginner-ish though.

When I switched to webdev, I dropped $20 on a system admin Linux course on Udemy. I highly recommended this approach.

https://www.lpi.org/our-certifications/lpic-1-overview/

Free PDFs, touches on the topics and actually shows you the commands, gives you exercises + further info. It will never be an end-all-be-all but it's a start if you're looking to learn something. It really all depends on what you're trying to get out of it I figure. If you're trying to be a sysadmin, then everybody else will have a different answer.

You are probably approaching this from the wrong angle. Linux, and computers in general, are tools. Figure out what you want to use it for, and then do it. One example would be to build a homelab with jellyfin and nextcloud.

On the path to that goal, you’ll find problems and tasks for which there exists very nice structured resources. For example, you might want some security, a perfect opportunity to read a book on networking and firewalls.

https://tldp.org/LDP/Bash-Beginners-Guide/html/

I'd look into used textbooks.

There is a great cheat sheet made by Ubuntu.