Wikipedia lists the "all swans are white" as an example for a falsifiable statement, but it is not practical enough. To prove that all swans are white would require to observe all the swans in the world.

Something being falsifiable and something being universally possible to check are 2 different things.

In theory you could falsify that statement after checking only a single swan if it happens to be a black swan.

Conservation of energy is falsifiable. If you found some way of creating energy without taking it from elsewhere then you would falsify it. However it isn't practical to check every cubic meter of space in the universe to check if it applies everywhere.

there's also the old Invisible Dragon example from Sagan

“A fire-breathing dragon lives in my garage.”

Suppose … I seriously make such an assertion to you. Surely you’d want to check it out, see for yourself….

“Show me,” you say. I lead you to my garage. You look inside and see a ladder, empty paint cans, an old tricycle—but no dragon.

“Where’s the dragon?” you ask.

“Oh, she’s right here,” I reply, waving vaguely. “I neglected to mention that she’s an invisible dragon.”

You propose spreading flour on the floor of the garage to capture the dragon’s footprints.

“Good idea,” I say, “but this dragon floats in the air.”

Then you’ll use an infrared sensor to detect the invisible fire.

“Good idea, but the invisible fire is also heatless.”

You’ll spray-paint the dragon and make her visible.

“Good idea, except she’s an incorporeal dragon and the paint won’t stick.”

And so on. I counter every physical test you propose with a special explanation of why it won’t work.

Now, what’s the difference between an invisible, incorporeal, floating dragon who spits heatless fire and no dragon at all? If there’s no way to disprove my contention, no conceivable experiment that would count against it, what does it mean to say that my dragon exists? Your inability to invalidate my hypothesis is not at all the same thing as proving it is true. Claims that cannot be tested, assertions immune to disproof are veridically worthless, whatever value they may have in inspiring us or in exciting our sense of wonder. What I’m asking you do comes down to believing, in the absence of evidence, on my say-so.