I installed nil and I only found it working in Kate (at least out of the box).
I tried a couple extensions for VS Codium, but they were nowhere near as useful as nil.
I also found nixd, but I’m yet to try it.
Do these programs require some special configuration to work on any editor or are they supported only by a handful like Kate?
Read the readmes.
It’s strange because I did nothing to make nil work in Kate, it just started automatically.
Some editors will work with them automatically, others may have to have them referenced. Checking the config options for your editor will let you know. I use them in helix and zed and it was shrimple enough to add and configure them.