Great question.
For me it would be if

• vaccination was mandated, would be punishable by law and you need that to have access to stores like supermarkets
• you're not able to sell your house due to insane climate rules
• if a government starts to deny you access to your drinkwater supply or limits it for whatever reason
• If your country is severely deteriorating: high crime rate, dangerous to be outside, extremely high taxes, agressive and violent racism/wokism
• Totalitarian regulation and laws

I get the feeling that the whole EU is something you don't want to be living in in about X years.