What is a button supposed to look like?

Buttons used to be easily identifiable. Not anymore. Some buttons today are not immediately identifiable as buttons. And with some it's unclear whether they are enabled or not. But the old buttons look strange to users today so I rather not use them.

So how do I correctly signify a button to users?

(I'm not referring to blue underlined hyperlinks, nor to icons at the top of the app like ⚙️✂?. Those seem fine.)