that can be done easy (for beginners) and can be played on any mobile device (IOS / ANDROID) ?

Games aren't easy and for beginners.

learn.unity.com

buy assets online

idk about easy but doesn't take a bunch of coding knowledge

Yep I made the original flappy bird

Man…. You got a long way to go

try modified roblox

Dude woke up and decided to make a videogame today

an online one at that

How much programming experience do you have? What kind of game are you making? Is it real-time, turn-based, how many players in an instance, etc? The fact that you're asking this means that you don't know how difficult netcode can be.

how much does the earth cost

'bout tree fiddy

It’s possible. Look up Unturned

I mean if you were to really commit to learning Unity and C++, you could realistically have something tangible in like a year.