Leaving NATO would mean closing US-bases in Europe overnight, not getting valuable intel from partners in NATO, jeopardizing US defense deals, and a million other things.
As always, it's grandstanding from Trump to get some extra bucks from his allies.
US pulling out of NATO would likely embolden China to make a move on Taiwan. Seeing how much of the US economy revolves around technology, I really don't think there's any other option than to defend Taiwan, as it stands. Sure - Europe also depends on chips from Taiwan, but they'd also be swamped in the Ukraine/Russia conflict.