As title. I have tried many ways on the Internet and read many threads on this forum. The most promising post is this one: Unity3D with vim - #28 by raining_day0513 (linked to my reply), in short, the picture describing my problem is the same as this reply on the same thread: Unity3D with vim - #18 by nscheurich
The other answers are too old and cannot be applied nowadays.
I’m using macOS 12.2. I build neovim from the source. I tried following this tutorial, Configure (Neo)Vim for Unity Game Engine Development (chrislabarge.com), to create a script that should be selectable when I hit “Browse…”, but the script dimmed out so I stuck.