Stephane Maarek got me a great head start on AWS stuff, and he's articulate enough that I was able to do it at 2x speed and understand the concepts.
Unfortunately, or forutnately, the training is reflective of the multiple-choice questions that the certification is presented with - so there is little to no practical deep-learning of the concepts. However, this allows the training to be concise and a good high-level overview.
These guys were instrumental in my Kubernetes knowledge, and I've had other people take their docker & DevOps courses and were happy with those too. I like that they maintain a real-world terminal that they spin up for their courses.
This is a free interactive course that I did pre-cert for k8s and I think it was both fun and a great exercise to speed up my troubleshooting of problems and implementation.
This is a great work of fiction that helped me better understand the role of DevOps in an organization.
This is the literal book on SRE.
And a TL;DR on implementing these bigger picture systems.
I really like this format of a skill-layout. They've got others that are similar but this is specific to DevOps. Don't let your eyes cross, it's meant to be consumed one at a time
Finally and certainly not least: Looking up any GitHub hosted, community curated, "Awesome" list. These are curations of topics to learn or explore based on whatever tickles your fancy day to day. When in doubt, try googling "Github awesome list <query>"