bash doesn’t know boolean variables, nor does test (which is what gets called when you use [).
A solution would be:
if $myVar ; then ... ; fi
because true and false are commands that return 0 or 1 respectively which is what if expects.
Note that the values are “swapped”. The command after if must return 0 on success while 0 means “false” in most programming languages.
SECURITY WARNING: This works because BASH expands the variable, then tries to execute the result as a command! Make sure the variable can’t contain malicious code like rm -rf /