Arduino Power Supply 12V

I want a power supply for arduino mega… 12v it’s okay?
I think arduino needs 1 A ? With 3.5a arduino breaks??

12V is on the limit of the recommended voltage. If it's a car battery, and goes up to say 14V that's dangerous. Also means even at 12V the regulator has to work hard to bring the internal voltage down to 5V and that generates heat.

The Arduino will only draw the current it needs. You can run it off a car battery which can supply 100s of Amps with no danger as long as the voltage isn't over the limit.

I think arduino needs 1 A

No, nowhere even close. It will take about 40mA.