Depending on your current skill level perhaps the following would help.
I would recommend getting a book on each of your interest areas of the stack and work through them ~2 hours per day per book.
eg: a curriculum could be:
- A book on linux, android, or iOS operating systems. Learn about filesystems, reading binary files, and at least one binary file layout to get a sense of "it's all just data" (Hexdump or C)
- A book on networking (learn all the OSI layers, practice working with the various envelopes, see them in TCPdump / Wireshark or other sniffing tools
- A book on internet like technologies eg: https://hpbn.co/
- A book on Frontend development. perhaps React
- A book on Backend development. Perhaps something about making HTTP + RESTful + JSON apis (alternative GRPC development)
- A book on a datastore of choice, I recommend postgres and you can grab the manual and books from here: https://www.postgresql.org/docs/
just my 2c of how I'd spend ~1 month per book offline but still progressing.
The hardest part is going to be the discipline to actually work at it every day consistently and for more than like 15 mins :)