There are several ways to disagree in English.

„I disagree.“
Clear and direct. Sometimes exactly what you need.

„I’m not sure I agree.“
Softer. It leaves more room for discussion.

„I see it differently.“
Signals another perspective without directly rejecting the other person’s opinion.

💡 Quick tip:
Being polite doesn’t always mean being indirect.

Choose your words based on the situation, your relationship with the other person and what you want to achieve.