CTRL+F hijacking is necessary in some cases when apps are not displaying the full text that the user would expect to search. E.g. when there's a 10K-line code file and the UI is not loading the whole thing into DOM, but the user would expect a "find" to search that whole code file.
Browsers can deal with very long documents. Ctrl+F works like a breeze on HTML that's 100K lines long.
Browsers only struggle to run heavy JS frameworks that wrap every line in a dozens of spans with dozens of handlers and mutate it all on every line scrolled.
This misses the point. Websites are allowed to replace default keyboard shortcuts for a reason. There are only a few exceptions to this, like Ctrl+W. In other words, you can design your website however you want, except to make it more difficult to leave. This is an implementation of the same philosophy.
So jarring when websites replace core functionality with their own broken crap because they think they’re special.
Some also seem to hijack right click menu now