Is 1) Nf3, The Strongest 1st Move?

Yes and 1) Nc3, cover the most squares on move one.

But Nc3 can be attacked more easily with; 1)...d5 2)...d4

c4 and d4 both have better odds at master level.

Wouldn't opening up lines for bishop and queen whilst controlling some centre squares be better? Like good old e4?

Nope. You would be advised not to bring out the Queen through there at all.

While the Bishop if moved with

Pointless aims at f6 from Black.

Which is why GrandMasters rarely play Bishop's or Guocio Piano.

But the Spanish/Ruy Lopez still remains promising. But entails 2) Nf3 First.

Nf3 is best according to the computer because it waits for black to show his cards before white. But from a human perspective, e4 and d4 are the best as they directly control and occupy the centre.

It technically doesn't matter what you occupy, but what you attack.

A lot of stuff that starts with 1.Nf3 ends up transposing into d4 and c4 openings. In fact, if your opponent plays 1...c5 you can even transpose to a Sicilian.

Nf3 feels too passive to me, dont know why

It's not passive. It just avoids some traditional lines which provide more chances of advantage. Nf3 is kind of a short cut to avoid lines but in return you also lose the ability to play some lines you like.

I think 1.Nf3 is the most flexible 1st move.

You could also just play the garbage Carlsen is using these days to beat up GMs, like a4 or h4 and other nonsense.