File system in linux/unix based distros

The LFS201 course has a few sections that pertain to filesystems. Specifically it covers the linux filesystem tree and layout, but it refers to the FHS https://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.pdf. Other details like formatting, partitioning, the use of modern vf, fs encryption, etc are all touched. While it's not close to being exhaustive, the information is manageable and I think it gives many readers an idea of easily available topics to pursue.

I'm in a similar boat- very fascinated how filesystems are structured and work. I haven't really exercised my interest yet so my advice may sound like a LFS201 sales pitch, and it in a way it is- because it's a good course, but really I mentioned it because "understanding filesystems" is a pretty broad aspiration that should be refined. Disk types, disk geomtry, virtual filesystems-- the list goes on and it's changed significantly over the years.

One suggestion I've read is to involve yourself in the development of a filesystem such as btrfs. I'm an advocate because while wiki's and articles are good information and seemingly important, dwelling on information from the past isn't always interesting and finding new (free) material on this topic I'm assuming can be difficult.