Task:
There are 2 buttons, when we hover the cursor over one of them, the second disappears.
The task needs to be solved only using HTML and CSS
without using javascript

Yes, this is a good solution.

Try to solve this without using the pseudo-classes :is() and :has()
You can solve this using only one pseudo-class :hover. Then it will be more cross-browser

*, button:hover {
opacity: 0;
}