How many stars are in the Leo Constellation? And how many planets are there in the Leo Constellation?

Impossible to answer. Leo is just the name for an irregular area of space from here to the observable limit of space in that direction.

Imagine how many individual grains of sand are in the Attacama desert

Then Add the Saharrah and the Ghobi Deserts

And all the rest of the deserts in the World, plus all the beaches Worldwide

Why not count in The Moon and Mars ?? For good measure

All done ??

Well you are not even at one percent !!

There are thousands of galaxies in Leo, maybe millions.

I would say, quadrillions of stars.

Lots, and nobody knows.

Our galaxy contains about 200 billion stars

Most of those stars are in the 13 zodiacal constellations.

So we could estimate the number in Leo as 200/13

Make it 200/20 = 10 billion

If one star in 10 has a planet ...

that makes a total of 1 billion planets in Leo.

https://en.wikipedia.org/wiki/Leo_(constellation)

There are millions of stars in each constellation, just in our own galaxy. At least 154 of them are considered "notable". There are 20 of these that are known to have planets.