shift-shift is the 42 of intellij editors, open files, rename things, import ordering, search class/function/method definition etc etc.
"shift-shift open" to open projects. next time it will probably be "shift-shift o" It also displays the actual shortcut.
Integrated terminal (and all other cases) switch focus to the editor: escape.
For all other cases: you are probably aware that you can change shortcuts. For example to vim shortcuts. Not 100% the same but still. And yes, switching editors take some time get used to.
(I love pycharm, i like VScode for small projects, dont like the un-integrated mess of for example spell check correcting function names?)
intelligent completion is something like cmd+mayus+space. "find usages" is cmd + f7 (which in osx means cmd + fn+ f7). The "open" dialog for opening a project doesn't even have a default shortcut, it's mouse based and will open a second dialog asking if you want a new window or just reusing the current one. CMd+mayus+f for global search wont work if my focus is on the integrated terminal, I have to click out of it.
I feel like I'm learning to play piano placing my hand in weird chord shapes constantly, and half those things launch an ui pane or menu that I practically need to navigate by clicking even if they sometimes technically allow some kind of keyboard interaction.
It's not like I'm an extreme vim+dvorak user obsessed with having everything in the home row at one button press, but a bit of thought into priorizing shortcuts and placing the common ones in comfy places would go a looong way.