When you save an expense that takes a budget past 80% of its limit, NEXO shows a Budget alert. You'll get another when it reaches 100%.
You're only warned once per threshold. Adding more expenses after you've passed 80% won't keep repeating it until you cross 100%.
Turn alerts off: Settings → Notifications → Budget alerts. Your budgets keep working, and you just won't get the pop-ups. This setting is saved on each phone separately.