This page of the Among Us guide explains what is the amongus.dev website and whether it is safe.
Amongus.dev is a website that lets players generate custom skins for Among Us. There aren't many of them, but they are really original. The problem is that this website is really just one big scam designed to rob you of your money and data. Everything looks legitimate at first glance – you choose the skin that interests you and click generate to your device.
The site then executes certain processes, and once they are finished, you will have to click Verify. When you click this option, you will see a window that will ask you to complete 2 tasks in order to get your chosen skin. It is, of course, a scam designed to take your money away. If you want to get skins for Among Us, buy them from the in-game store. To summarize, amongus.dev site isn't safe. You will get nothing from it, only lose money.