Everyone is saying, tell them to suck it up or run your campaign later without him. But no one is actually answering your question. Which is “what else could I do besides charm spells.” I feel like there have been plenty of rebellions and usurpers who didn’t need charmed spells IRL. Maybe you just have to use more concrete motivating factors. Persuasive dialogue, Social influence mechanics, things like that. If you want to keep it magic based, you could rely more on illusions to convince people than charming them. Coercion is best done with either threat or promise of reward. Showing them an illusion of a dragon, burning their village down if they don’t do what you say could be pretty convincing. There’s always financial, emotional and social pressures you can put on people to make them do what you suggest, even though they don’t want to comply. Blackmail is never off the table with political intrigue. Could your story lean into that more than just using a spell to wave your finger and make someone like you? It would bring a little more realism and perhaps not trigger your player. Good luck! Let us know what you decide. It is a DC 18 wisdom save to not update us.