“Ignore the behavior” is a radical oversimplification. A better approach would be to make sure you’ve developed the skills in yourself to remain completely calm and unaffected when a tantrum happens, then you make yourself present but calm and uninterested until the child calms down, at which point you immediately reward them being calm with affection and attention, or whatever it is they would perceive as a reward. Without the reward part, ignoring a negative behavior risks worsening it over time. Also this is clearly not always possible, eg if you’re in a public setting or if the child is doing something dangerous.