There was a small popup just when i imported a photo, that let me remove background in 1 click, it i

It’s probably the Contextual Task Bar. If it comes and goes, that’s because it depends on the context (what’s selected), so it will show a Remove Background button if you select a pixel layer like a photo; see the demo below. For example, the Remove Background button won’t appear in the Contextual Task Bar if you select a type or shape layer, because removing the background doesn’t make sense in that context.

If the Contextual Task Bar doesn’t appear when you select a pixel layer, choose Window > Contextual Task Bar to enable it.

The end of the demo shows that you can also get the Remove Background button by selecting a pixel layer and looking in the Quick Actions section of the Properties panel. If you’re working on a small screen, you’ll probably need to scroll the Properties panel to find that section at the bottom.

So there are really two ways to get the Remove Background button, if a pixel layer is selected.