most of the material i see is written for people that want to write applications that work with postgresql, not on how to proficiently manage postgresql itself.
EDB has a fairly comprehensive set of self-paced trainings for sale. I went through them and thought they were really good.
Postgres documentation is excellent though, and though the docs are long, reading through it carefully should give you almost all the information you need for most database tasks.
Then practice, docker makes this easy.
But there is a great book on the internals (very long, in depth, but not unreadable if you have a good foundation already) - https://edu.postgrespro.com/postgresql_internals-14_en.pdf
They probably have newer versions, this is just what's in my bookmarks
Happy to help with more targeted recommendations!
I work as a system engineer / devops engineer / infrastructure engineer. I often need to keep postgresql up and running, ideally in a smooth and performant way.
I don't like tool-specific tutorials or storytelling-based articles.
I'd like to learn the core postgresql things (terminology, tasks, operations) so that then i can evaluate autonomously what tool to pick and why, rather than following the trend of the month. And of course, being able to actually do "the things".
Ideally, the next progression of this would be being able to understand postgresql performance and how to tune it (again, in an holistic manner).
Per my understanding, this is the kind of skills that a DBA should have. Some of it overlaps with the skills of a decent developer (i understand that).
I'll take a closer look to the material, which is already good.
It's sad that there does not seem to be anything past "DBA1" (that is, no DBA2 or DBA3).
There's some stuff for internals (mentioned in a sibling comment), as well as what seems like stuff for PG15 though I haven't looked at it.