I’ve created a pull request that improves the Find in Files performance by re-using the existing approach with several optimizations, and thus making it 2…3 times faster.

https://github.com/notepad-plus-plus/notepad-plus-plus/pull/18376

I haven’t invented anything new, just optimized what was already there.
I realize the code review may create an impression that several parts have been completely re-written, but that’s no true.
In fact, the existing code has been refactored by extracting parts of several functions into separate helpers, so these moved blocks of code together with new helpers create an impression of a lot of changes. But if you follow the code logic, or just manually copy-paste the separate helpers into the places where these helpers are called, you’d realize the code flow remains the same.
Please feel free to review and test.
I’m writing here because I’m afraid the longer this pull request remains open, the higher are chances of merge conflicts to appear in the affected files.