So now the question is bitcoin safe from hackers?, can it be stolen?
This is subjective because the answer relies on the capacity of the owners to protect their coin but assuming the owner will 100% guaranteed to do their part to properly keep their Bitcoin on a non custodial wallet then the answer is Bitcoin can’t be stolen.
No hackers can brute force someone else private key as it will take a lot of time of power just to hack someone else private key. This discussion was discussed already in the past.
Here’s the explanation of @Blackhatcoiner on the probability of hacking someone’s private key.
The odds of guessing someone's private key... Let me put it in this perspective. There are estimated to be 7.5 quintillion grains of sand in the Earth; that's 7.5 x 10^18. Now ignore the shape of our solar system, and make the hypothesis that there are a trillion clones of Earth, spinning around the Sun. That'd make the total grains of sand in our Solar system about 7.5 x 10^30. Stupidly large number there. Imagine if I told you to guess my chosen grain of sand, across this uncountable set of grains, and that I picked one at random, maybe at some corner of an ocean from Earth #623,546,123,002, or at a replica of Egypt from Earth #881,239,303,566.
Guess what. The number of these grains are not even the 0.0000000000001% of the total valid Bitcoin private keys.