in [[ there is generally no need for quoting, except the right hand side of an = comparison

in [[, empty strings are falsy, so this also works:

[[ ! $VARIABLE1 && ! $VARIABLE2 ]] && echo "OK"

The variables need a dollar sign: $VARIABLE1

help test shows what -n and -z do.

Never use a && b || c. It is not the same as if a; then b; else c; fi: when a succeeds but b fails, it will run both b and c.

I would not bother with [ unless you absolutely need compatibility with non-bash shells.

no I don’t have that choice, see my other comment

This, except I won’t buy an apple device (unless forced to: in Germany an i-bad is required in many high schools, yes you need to pay for it in full with your own money, yes it needs to be an i-bad they even require a specific model)

Some employers offer intellij ultimate subscriptions. It’s even mandatory in some teams. The devs don’t have to pay out of their own pocket. But I think many of them are hooked and will lobby to keep the subscription going.

Try opening a terminal an typing echo 'Hello World!' My two cents: You can forget about Linux for a while. Using a terminal is more important. Here’s a classic guide: https://mywiki.wooledge.org/BashGuide