Linuxcommand.org is a great start. Writing shell scripts and using cli programs for things you actually need and will use will greatly accelerate learning. I stopped using a file manager entirely to force myself to learn how to get around, then switched to neovim from vscodium, taskwarrior instead of Obsidian Tasks, termdown for timers, etc. A tiling wm makes the transition easier imo because you can have many terminals open for visual multitasking. Like with anything, you'll get better faster if you just do it a bunch and don't be afraid to mess up and get your hands dirty.