I'm partial to pcmanfm-qt, which also supports splits, and has the best "search in current directory" I've seen anywhere. You open a directory, start typing, and it filters out matching files fzf-style.

It doesn't simply select them like some other file managers do, it searches within the name and not just the prefix (again, like some other file managers), you don't have to press anything beforehand. When you get used to it, it's hard to go without it.

https://github.com/lxqt/pcmanfm-qt

For those preferring lightweight environments, it has far fewer dependencies than dolphin.

Wish there was a screenshot of the final product in this repo! QT apps are non-trivial to build if you don't already have the environment setup.

BTW, do you know if it can build for macOS, or is that a non-starter?