I'd say give a few dozen orders of magnitude.

Assuming the human race has spread across multiple planets in the next 10 billion years, lets give a generous population estimate of 1 trillion individuals. Even if every single one of those 1 trillion people generates 100 new bitcoin private keys every day (why anyone would need that many I don't know) for 10 billion years, we are still only talking about (1 trillion * 100 * 10 billion * 365) = 3.65*10²⁶ keys.

For OP, even in my hypothetical scenario above, we would still only have generated approximately 0.0000000000000000000000000000000000000000000000003% of all possible private keys. If we continued to use bitcoin for a trillion trillion trillion years, then we might have to start worrying about collisions, but given that all the stars in the universe will die in only 100 trillion years, we will probably have more pressing issues to deal with.

Only if you are silly enough to pick your own seed phrase or use a brainwallet. If you use a proper randomly generated seed phrase, the chances of someone guessing it are essentially the same as the chances of someone generating the same seed as you, as has been outlined above, i.e. never going to happen.