A Bitcoin private key is simply a number between 1 and 2
256To put that number into perspective, 2
256 is roughly equal to 10
77. The estimated number of atoms in the entire observable universe is about 10
80. That means there are nearly as many possible Bitcoin private keys as there are atoms in the universe.
If you had a supercomputer that could guess a trillion keys per second, and you had a trillion of those computers, and they had been guessing since the Big Bang (13.8 billion years ago), they wouldn't even be a fraction of a percent of the way through all the possible combinations.
It's your responsibility to keep your private keys safe.
Maybe run your own node. You can do a small home setup with a raspberry Pi and something like this from gekkoscience

As for safety of funds for the long run, always use cold wallet. And for the fancy
BTC enjoyers
We have
https://icarus-cards.eu/