You could always online stalk them, even though that's pretty creepy (kidding)

I'm the lazy person who is too lazy looking for another way. I'll just directly ask the person if s/he is single 😂

You might find that people who are not single show no signs of it when the respective partner is not around. In rare cases they don't show any hint of it even with their partner around. But I guess most will show some sign of being not single when you try to flirt with them. In your case that might be an option to find out?

I'd just ask them.

"Hey I think you're really cute, here's my number ☺️" Wish them a good day and then disappear from the earth forever