As you've guessed already - if there was a straightforward way I wouldn't be asking. :D
You'll just have to explain the meaning, because this expression doesn't exist in Hebrew.*

So - what is "a win-win" situation? It's a situation when all sides.... win?
⮞ מצב שבו כולם מנצחים? (audio #1)

We could say it this way, but I'd argue that it would sound better if I dive deeper into the implied meaning and say that it means "both sides benefit."
And how would we say "benefit" in Hebrew?
That's an interesting point here! We don't have a dedicated verb for "benefit," we use the "to earn" verb instead! That is - להרוויח.
So, "both sides benefit" -
⮞ שני הצדדים מרוויחים! (audio #2)

More examples:
⮞ It's a win-win situation! זהו מצב שכולם ירוויחו ממנו (audio #3)
⮞ Do as I say and it's a a win-win! תעשה כמו שאני אומרת וכולם ירוויחו! (audio #4)

And even these
would work very well as an indirect way to transmit the same meaning:
⮞ It's a winning combination - זה שילוב מנצח (audio #5)
⮞ It's a sure success! זאת הצלחה בטוחה! (audio #6)

*I saw in Reverso some suggestions, but I don't agree, it's not commonly used. :D