For any intention, thought, or decision you make in your mind, there must have been prior brain activity that determined it, because there’s no other way you could have developed a thought.
Another option: there are cases where the thought is the brain activity. You’ve still got a ‘ghost in the machine’ with thoughts being something other than embodied brain activity capable of leading to action.
A better grist for this thought experiment might be something like planning a vacation, planning a move in a complex game, or figuring out what graduate schools to apply to. Games are probably the best example because they’re a pocket universe of sorts that provide an objective, rules to define all paths forward, and hence the motivation to think things through.
Quoting Libet, “ “Given the issue is so fundamentally important to our view of who we are, a claim that our free will is illusory should be based on fairly direct evidence. Such evidence is not available.”