The biggest lever to appearing confident on stage isn’t body language. It’s saying what you mean.
When we don’t believe in the words we use, it will almost always feel at least a little weird because our body wants to do one thing (according to what we actually believe in) while our brain wants it to do another thing (according to what we pretend to believe in).
Most of us are not professional actors. If you lack confidence in your words, you’re not just going to trick your audience with one or two hacks from the last body language workshop. (And let’s just face it: even some professional actors aren’t that good at it.) While most audiences are not body language pros, either, most are pretty good at sensing a mismatch between what our body does and what our words say. They probably can’t pinpoint what’s off exactly but they can somehow sense that something’s off.
That dynamic changes when you switch to saying what you mean, using words you deeply believe in. It won’t magically turn you into a confident speaker, but it will give a much greater impact to anything you do to amplify your message, mostly because message and delivery will be consistent.